PC going to Sleep Mode randomly.

I have been having this issue that my PC keeps going into sleep mode at random time. It could be in the middle of a game, or watching a movie, surfing the web, or when I am not doing anything on it. Sometimes its an hour between sleep modes, and other times 2 days. I have disabled the sleep mode function in Windows 7 Power Management section. I recently upgraded my tower and motherboard, and also performed a fresh install of Windows 7 after formatting the HD. I have googled the issue and only keep finding answers such as turning it off in power management section or maybe temperature related issues. I use Speedfan and monitor my PC at all times, the only thing that get high temp is my GPU and that hit a max of 74 C°, CPU hit a max of 54 C° and mainboard and HD only 35 C°. Its really starting to get annoying and would like to find a solution. My PC specs are listed below. Any help will be greatly appreciated. All drivers are up to date.

Tower : Cooler Master Cosmos II Ultra Tower
CPU: QuadCore Intel Core i7-2600K
Mainboard: MSI Z77A-G43
GPU: Gigabyte GTX 770
HD: OCZ-AGILITY3 120GB SSD, ST1500DM003-9YN16G 1.5 TB, WDC WD10EACS-00ZJB0 1TB
RAM: G.Skill RipjawsX DDR3-1600 DIMM 8GB