GPU crashing

I bought a gt240 a couple of months ago and had a problem with it cutting out and the game I was playing would crash. Since then I have changed my OS, installed a new PSU and installed a new motherboard. Now the crashes are worse than ever... The whole screen turns to crazy colours and the computer completely stops responding.
My temperatures are all fine btw.
My set up is now

Inno3D GT 240 1GB
AMD dual core processor
Antec TruePower 650W PSU
Gigabyte GA-M68M-S2P with onboard GeForce 7025

I also have 2GB of RAM, not sure the manufacturer

So, am pretty tired of spending money and getting nowhere. Any ideas?

Also, it crashes only when i've got the graphics card in, remove it and everything's fine. The crashes happen as soon as anything demanding happens on screen... even in the lowest graphics mode. I've been doing work in 3ds max and UDK recently and have found things like adding a sky box will instantly cause a crash

 

Can you swap out the graphics card for another one to see if that's the problem?

 

haven't really got access to another one. could only ask mates and doubt they'd be up for bringing theirs round. problem is, on the basis that it's not the graphics card what else could it be? could faulty ram do this?

 

Faulty ram can manifest itself in all kinds of weird ways that are non-intuitive. You can try a RAM testing program such as Memtest86+ to see if your ram is OK. It's a utility you have to burn to cd, which you then boot from. I;m assuming you know how to burn an ISO file?
Memtest 86+ can be found here:
http://www.memtest.org/#downiso

 

in the middle of a hardcore lan football manager session at the moment but will definitely give that a go. thanks