Check to make sure that the cooling fan for your cpu (processor) is running. The computer will shut down without warning or error notice to protect the cpu. If this started when you reseated your graphics card, then I'd start there. Remove your graphics card. Make sure to unplug everything from it too. Now put it back in and ensure that you have it seated correctly and tightly, and that any/all wires/cords are plugged into it correctly and tightly. Start your computer and keep your fingers crossed. If it still acts up, then keep reading.
IMPORTANT: Be sure to ground yourself on your computer case either by touching the silver metal frame of the case or by using a wrist strap. A tiny static shock can ruin any piece of hardware in the computer.
Remove the following (yes, all at the same time):
1 stick of ram, unplug cd/dvd drive, remove pci adapter (wireless adapter if you can), remove graphics card (plug your monitor into the VGA spot on your motherboard, and you should get the glorious 16 bit graphics) and unplug/remove anything plugged into USB or firewire ports. Now, try to start your computer and see what happens. If it works, then start adding things back one at a time, with the graphics card being last. If you install or plug something in (like a stick of ram or the graphics card) and the computer won't run for more than a few seconds, then you know it's that last piece that you tried to install/plug in. If when you have everything out except for the single stick of ram and it still won't run for a few seconds, then put that stick in the other slot. If it still does it, then remove that stick and put the other (second stick) back in. If it still won't run, swap the slots again. If it still won't run, then you know that it's something other than your hardware components (like your motherboard/cpu fan etc. etc.).
Of course, if the computer is still under warranty, then I'd back up things on my hard drive to DVD or CD or an external hard drive and let them deal with it.
just summed up my last sentence there perfectly!
Edited by stevealmighty, 20 June 2007 - 04:15 PM.