Upgraded to 7850 cannot boot up

[Prydeful]

Hello all. I just purchased the Radeon 7850 Sapphire and upgraded from my nvidia GTX 460 Cyclone. I installed the latest drivers and rebooted. After that I tried to play Dota 2 and it wouldn't run so I rebooted again. Unfortunately after I get past the blue icon loading screen (I am using windows 8) the screen goes black and then starts to flicker. I went into BIOS settings and turned everything to default but no dice.
Does anyone have an idea? Thanks!

 

[prodriver2]

system specs please.

 

[Prydeful]

Ok!
OS: Windows 8 64bit
Motherboard: Asus M4A88t-V EVO/USB3
Sound Card: Soundblaster X-Fi
Internal HDD: Deskstar 500Gb 7200RPM 16MB/Mo cache
RAM: 8gb
CPU: AMD Phenom(TM) II X4 955 Processor 3.2 GHz << Corsair Liquid cooling attached
GPU: Radeon 7850 Sapphire

Anything else?

 

[Prydeful]

Update!!! So, I decided to test a theory, I unplugged the power from my 7850 and plugged my cords into my onboard video card. Lo and behold, I was able to log in, so it was my graphic cards problem. I had previously messed with some graphics options in the Catalyst Control Center, so I returned everything to default, rebooted and plugged back in my 7850, and it worked. Will now try playing a game, but I still don't know why my video card decided to stop working...

 

[prodriver2]

What PSU (power supply) do you have? It may be that your graphics card needs more power which your PSU cant handle.

 

[Prydeful]

The thing is, I upgraded from the 460GTX which required more watts than the 7850 so... I don't think the PSU is the problem, I have about 80 watts spare.