Mac Pro - Usually wont boot, sometimes will. Need advice

Sounds like you need to replace the GPU. I suggest Apple's ATI 5770 - $249.00. An excellent and far less troublesome GPU than the Radeon card you now have.

Your system needs more than old 4 x 512MB

8GB kit goes for $64 now and run better

Did you post what gpu you have? the X1900 has to be pulled and cleaned and does not work with 10.7.5, the 7300GT pretty much the same. And 8800GTs also have trouble.

Heat kills FBDIMMs and they don't last 5-6 yrs and that system is going on 7.

There was no X1950 from Apple, only 1900.

ATI Radeon 5770

http://store.apple.com/us/product/MC742ZM/A

http://www.amazon.com/Apple-ATI-Radeon-5770-MC742ZM/dp/B003Z6QH6M

http://www.bhphotovideo.com/c/product/726537-REG/Apple_MC742ZM_A_ATI_Radeon_HD_5 770.html

How To Install and Remove Memory Mac Pro

https://support.apple.com/kb/HT4433

2x2GB FBDIMM DDR2 667MHz @ $32

http://www.amazon.com/BUFFERED-PC2-5300-FB-DIMM-APPLE-Memory/dp/B002ORUUAC/

X1900

http://www.xlr8yourmac.com/Graphics/X1900XT_Overheating/ATI_X1900_artifacts.html

http://www.xlr8yourmac.com/Graphics/radeon_X1900XT/X1900XT_dust_buildup.html#sto rytop

I have heard before "I don't need more than 1GB or 2GB." And I know how OS X and Safari and every app works with low memory or with adequate and yours is on the anemic starvation under nurished side. 512MB DIMMs are also a problem.

RAM can do funny things. And with a 7 yr old system, and seems you were not cleaning out the dust and pulling the X1900 enough, like 3-4x a year, it has more chances of "old age" compared to if it was maintained.

FBDIMMs use to run too hot, needed extra cooling, and dust blocks them from releasing heat. When a system goes to sleep the heat inside actually builds, it does not cool down. Which is why when you restart it should and will run the fans at high speed at first on start or wake from sleep.

I can upgrade and get Mac running fast and smooth, but not in the configuration it is in.

But there is no majic answer I have other than treat everything as possible cause and start from scratch on everything. SMC Reset. Maybe new PRAM battery - I never do. Inspect parts and how they look.

My Mac Pro 1,1 runs better today with upgrades and such and clean install of Lion (I do recommend going to 10.7.5) along with RAM (I needed more than 8GB when I started using iPhoto a lot along with everything else). The SSD made it FAST - 10 seconds after login for 12 programs to be open and ready to use, 10 seconds to boot (rare ever do).

With any system bought used of course I would be careful, they may not have understood what to do and how to do it. But first thing to do is install a new hard drive and fresh OS.

Couple things to monitor temps, get dust out, etc and kick it into high gear. SSD is good no matter what and for this or another system (need Icy Dock adapter to install into one of the drive bays $15) But CLEAN out dust everywhere, with care, CLEAN OS and keep the FBDIMMs below 70*C you may need to boost the fans to 900 rpm - until you replace the X1900 and get at least one set of the Amazon linked RAM.

SSD: Samsung 840 128GB

http://www.amazon.com/Samsung-Series-120GB-internal-MZ-7TD120BW/dp/B009NHAF06/

WD Black 1TB $85

http://www.amazon.com/Western-Digital-Caviar-Internal-Desktop/dp/B0036Q7MV0/

WD Green 3TB $149 - (might want WD RED NAS/RAID 3TB though)

http://www.amazon.com/Western-Digital-Caviar-Green-Desktop/dp/B004RORMF6/

Sonnet Technologies Tempo SSD 6Gb/s SATA PCIe

http://eshop.macsales.com/item/Sonnet%20Technologies/TSATA6SSDE/

Resetting the System Management Controller (SMC)

https://support.apple.com/kb/HT3964

General Help

http://pondini.org

Final Cut Pro X, Motion 5, Compressor 4: Graphics card compatibility

http://support.apple.com/kb/HT4664

http://www.apple.com/finalcutpro/specs/

Temperature Monitor

https://www.macupdate.com/app/mac/12381/temperature-monitor

http://www.bresink.com/osx/HardwareMonitor.html

SMCFanControl 2.4+

https://www.macupdate.com/app/mac/23049/smcfancontrol

UPS

http://www.amazon.com/CyberPower-CP1500PFCLCD-Compatible-1500VA-Tower/dp/B00429N 19W/

Metro Vacuum ED500 DataVac 500-Watt 0.75-HP Electric Duster 120-Volt

www.amazon.com/Metro-Vacuum-ED500-500-Watt-Electric/dp/B001J4ZOAW/

Those 512s run hot as said, are old, and OS X and apps will use what there is, so even if you monitor pageouts and don't see any, take Safari it will use more if there is more available, up to 1.5GB RAM.

The requirement for SL was 2GB minimum and the number of people complaining their system is now slower... I can't force you and you can't tell until you have say 4GB or more, plus OS X is a "put apps in the background so they are there and don'[t need to be relaunched"

I don't do that much but 3.5GB is always used, Safari can climb to 2GB, even iTunes, and then there is 1GB just for iPhotoi. I often find it using 7GB (50%) and 14GB (20%+).

When I bought my first 1GB of RAM it was $300, 2x1GB was $400. Today 16GB is $128.

No you aren't using the video card during VNC etc

The best $100 is a SSD boot drive. Data on 1TB WD Black. $64 RAM and video card and you will see what your system is really up to. If you wanrt.

isn't that card still making the video going over VNC?

The key subsytem on the card is the screen buffer, which holds the data to be displayed. It is written directly by system calls from the CPU and through system calls that invoke the display processor (a numeric processor on the display card that crunches the data around to generate transforms on that data).

There is also some really fast (and runs hot) digital logic to read out the screen buffer and display the picture locally. That display logic fetches the data out of the screen buffer, converts it to the fast serial form required to paint the local screen 60 to 120 times a second, and whips it out at very high speeds onto the display interface again and again and again.

The display-painting logic is the part most likely to fail. If it does, you can use VNC all day, and everything seems fine, while your local display stays dark.

Another failure is the numeric transform engine on the display card. When this fails, system calls that use the full Driver will fail, but the calls used for Safe Mode, Recovery Mode, and stand-alone Installer will work fine (but not be accelerated).

To show a picture under Mac OS X, a display card needs EFI firmware, as all Apple brand cards (and some flashed cards) will have.

A card made for a PC, with only BIOS firmware, generally does not show a picture under Mac OS X.

There is a forum site that deals a lot in what PC cards work best, and you're "early Mac Pro" (pre-2008) firmware as well as whether whatever you do use will be affected by the PCIe 1.1 2.5GT/sec bandwidth constraints.

6870 vintage were popular. GTX 460 as well.

The darn site seems to 'spawn' lots of popup ads so I am not linking to it and not sure what is up but I hot keyed out of netkas immediately.

You have a first generation Mac Pro. The best GPU you can run in it is the ATI 5770. Anything more is a waste of money because you cannot take advantage of the capabilities with only a PCIe 1.0 bus.

http://barefeats.com/wst10g3.html

http://www.barefeats.com/wst10g5.html

Overpriced for what little difference between 5770 and 5870 in PCIe 1.1