Video card V motherboard

Hello,
I recently installed an "ATI Radeon HD 2600 Pro AGP 512MB DDR2 8X" video card on my Asus P5P800 motherboard. My computer is 5yrs old, has a P4 3GB CPU & 4GB of RAM. I only play RTS games so the it doesn't get much of a work out unless I start messing about with the 3D stuff in Inventor 10 (a design program) & I don't even know how much of a drain that is on the system. Everything seemed to work o.k. for a while & then the screen started freezing & the machine started showing signs of the CPU &\or the RAM overheating. On reading the book for my motherboard (& yes, I realise how clever it was to read the book afterwards), I find that the board only supports 1.5V & 0.8V AGP vidoe cards. I don't seem to be able to find out what voltage the card draws through the AGP slot. I know the card is working properly, because I tested it in a couple of other machines. My machine on the other hand will only run a card that I know is faulty (it could fine for 5 minutes or 5 days). I've tried half a dozen that work fine in my friends computers & 2 brand new ones. Could the HD 2600 Pro have pulled enough juice through the slot to damage it? Any information or advice greatly appreciated. Thanks.