I installed a HD Radeon 5570 card last year and it was working fine (appreciate its not the best of cards) until a few weeks ago when my pc shut off whilst using Flight Sim 2004 and would not turn back on.
After trying a couple of things with no luck, I took out the graphics card and it turned on (this is silly thing to do but i tried inserting it after I had turned the pc on and it might as well of been an 'off' switch...pc just went dead when it clicked in the slot). In my mind, it is one of 3 things.
1. The graphics card itself is faulty/damaged and causing the problem.
2. The pci-e slot on the motherboard is faulty/damaged (meaning a new motherboard is needed).
3.My psu (only 300w) has degraded and can now not power the graphics card along with the rest of the motherboard.
Any help on whether I am in the right ball park with any of my 3 theories or any other possible causes would be greatly appreciated.