So I got home from work yesterday and went to turn my computer on as per usual to be greeted by this:

The screens remained black, so I rebooted; I go as far as GRUB before my screens went black again. I rebooted again, they didn't turn on. I rebooted again, I got as far as the windows login screen.

This time I unplugged it, opened it up and cleaned it but to no luck. The GPU was still being tempermental. I repeated the process of turning off and on several times until one time it work as normal. I happily played games for the rest of the night (5-6 hours?) thinking everything was jolly good now.

Well I get home from work today and it is doing the SAME thing. Sometimes everything displays normally for a few seconds to minutes then the screens go black; then sometimes the screens don't come on at all.

Summary and additional points

• Screens sometimes turn on before shortly turning off, sometimes they don't; I cannot seem to determine any pattern between when they do or do not turn off.
• The build has been working fine for about 8 months now so I know it's not hardware incompatibility.
• If I plug a monitor into the on board graphics I can use the PC normally (just in low graphics mode)
• I have two monitors and it's a case of they both turn on or not. So I think I can rule out the monitors being dead.
• I have tried replacing the GPU
• I have tried replacing the RAM
• I have tried flashing the CMOS
• I have tried cleaning the inside
• The GPU is a Radeon HD 7870

My questions

Is my GPU dead? It's not very old and I would rather have a method of being certain it's the GPU before I fork out some money I can't really afford.

I do not have a second PC here to test it in.

If my GPU is dead why does it sometimes work and sometimes not?

Update

Okay, it was working again.. at least I thought it was. I left it running for 10-20minutes with the screens black. Turned it off and straight back on and it worked for all of 10minutes. I was then updating the post in joy thinking I could play some games for the rest of the night when BAM it went black again. So yeah, I don't know :C