Mac Pro early 2008 wigging out

The two built-in Ethernet ports on that Mac are Gigabit Ethernet capable. Unless that card you added goes faster, that card is not needed.

The Apple-firmware 5770 is often recommended. Drivers are in 10.6.5 and later. There are lots on the used market, and it only requires one aux power cord. If budget is really tight, you can use the Apple-firmware GT120, which is not much of a card, but does not require any aux power cords.

When you replaced the GT 8800 with the older card did your graphics issues disappear.

The Nvidia GT120 512MB card was the default card supplied with the MacPro 2009 and 2010,

it will work in the 2008, I have one as a back up if my Nvidia GTX 680 fails.

The GT 120 is the cheapest card you can get about £60-00 used her in the UK.

Make sure it is the Apple version, the one with the light grey cover.

As mentioned it is not a high end card so not suitable for 3D modelling,

High Definition video editing or other high intensity graphics work.

The RAM modules you took out, did you make sure they were seated correctly on the riser.

When I decide to clean my mac of dust and take out the RAM risers and remove the RAM

the mac can sometimes not register certain modules when they are put back in and restarted.

Simply powering down and checking that the modules are seated correctly and the RAM risers

have been slowly but firmly slotted back in can make the difference.

RAM modules need to be installed in a certain order so make sure you are doing that correctly,

read this guide here.

https://eshop.macsales.com/tech_center/manuals/Memory/macpro.pdf

This is the Apple Nvidia GT 120.

Pity you bought an Nvidia GT 8800 graphics card, when the Mac Pro 2008 was new on the market the GT 8800 was a build to order option, it was noted this card was prone to failure fairly early on.

My Mac Pro 2008 had one from new and I was very lucky that my GT 8800 lasted for 7 years before failing.

By the flickering screen it could be the graphics card is faulty, make sure it is seated firmly in one of the two lower

PCIe slots which are 16x speed and also there should be one auxiliary power cable from the card to the

motherboard.

There is also the question of the RAM you bought, it is very important in the Mac Pro 2008

that you buy the correct RAM it must be 800MHz DDR2 FB-DIMM with large heat sinks.

Was the RAM you bought certified as specifically for the Mac Pro 2008, and thus reassuringly expensive.

Click here for more info,

https://eshop.macsales.com/shop/memory/owc/apple-mac-pro/2008

With the side door off power up your mac and tell us if any red LED's stay lit on the RAM risers when

the mac boots up. Normal operation is for them to light up and go out almost immediately you start the mac up.

If any of the LED's stay on then there is a problem with the RAM, you get an idea of which stick are causing a problem

by which LED is still lit.

What happens when you take out your new RAM and only operate the mac with the factory installed Apple RAM.

read this article about Error correcting code RAM:

User Tip: Mac Pro and Error Correcting Co… - Apple Community

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