GeForce GTX 580 issue - no VGA detected

Hi,

I am having problems with my machine. I bought it last year from overclockers and below is the full set of specs they sent me

Titan 7300i Intel Core i5 2500K 3.30GHz @ 4.40GHz DDR3

GX-146-OK OcUK GeForce GTX 580 1536MB GDDR5
SW-127-MS Windows 7 Home Premium 64 bit OEM
MY-094-KS Kingston HyperX Genesis Grey 8GB 1600MHz C9
HD-040-OC OCZ Vertex 2 50GB SSD
CA-055-CS Corsair Graphite 600TM Midi Tower Mesh Windowed Case - Black
CA-056-OC OCZ ZS Series 650W '80 Plus Bronze' Power Supply
CD-099-LG OcUK 22x DVD±RW SATA ReWriter (Black) - OEM
HD-364-WD Western Digital Caviar Blue 500GB SATA 6Gb/s 16MB Cache -
OEM (WD5000AAKX)
HS-010-XG Xigmatek Dark Knight CPU Cooler
MB-364-GI Gigabyte Z68AP-D3 Intel Z68 (Socket 1155) DDR3 Motherboard
CP-365-IN Intel Core i7-2600K 3.40GHz

Basically sometimes when I try and start up any games or video files (with VLC Media Player) my monitor turns off and says no VGA detected. The cables are plugged in correctly. I also notice a few seconds after that the game volume stops working but the machine is still on.

Sometimes it doesn't even let me get past the windows loading bar and I have to go into safe mode. I have not done any driver updates in months, tried doing that and it didn't help.

Due to the game volume stop working I am starting to think it's a issue possible with the power supply? but the machine remains online so I have no idea.

Also if it helps I notice when in World Of Warcraft it will only crash when entering a new zone (loading bar)