Mac Pro 3.1 won't boot

A couple of weeks ago i turned on my mac pro and it didn't boot!
The video card fan whirls around for about 5 seconds and clicks off.
After looking around this forum and others for a while i thought it might be a power supply issue. So i took the tower to my local Apple repairer to get fixed. I called a week later to find out what the deal was and was told that its not the power supply and they were still looking at it. A few days later i got a message saying that it had bad ram and was fixed. leaving me 2gig of ram down (i had 8 gig of ram leaving me with 6 gig) and $75 out of pocket.
No sweat!
About a week later it did it again! Not booting!
i push the power button a few times and it booted! Phew!
It did this for a couple more weeks. Not booting sometimes. A few pushes of the power button and away we go.
Until of course i had a recording session booked and the mac pro would not turn on at all!
I've taken all the ram out (8 1gig sticks) and just installed 2 gig at a time. Going through all of them. Even the one the repairers said was bad. With no luck. I've reset the SMC and take the battery out and put a multi meter over it and it seems fine. (I must say that one day the screen went all weird. Kind of like blurred checkers for a minute but came good again.) I tried to boot it up without the graphics card, no luck!
I'm not sure what i should do??
Take it back to the repairer for another $75 or buy some more ram and see what happens.
Is it possible that ALL the ram is stuffed?

Is it possible to boot up without the video card?

Any advice you guys could give me would be greatly appreciated.

Thanks heaps
Damien