[Crash] Client will crash at beginning or end of random matches.

Computer specs CPU: AMD FX 8core Memory: 24gb (2x4gb 2x8gb) Ram VideoCard: EVGA 2gb Nivdia GTX 760 Gigabyte MB 1xSSD 2xHDD Windows 7

I recently upgraded my computer from an ASUS MB and I've been getting crashes at the beginning of the matches which crashes my whole system to the point that I have to restart the computer. I reinstalled LoL and I just recently played a game and it crashed when the Victory animation came up. Now I've been getting a crash toward the end like that with my older system but it never got to the point where my whole computer crashed. I've read of similar issues in the forums but they were either outdated by like 3 years or there was no fix.

Questions: Does anyone else experience this issue Has anyone ever fixed this issue

Things I've tried: Stress testing CPU, Memory, GPU - All passed reinstalling LoL Update upgraded to windows 8.1 fresh copy only LoL and Curse voice installed (no firewall/antivirus) and I played two games fine until I decided to play a custom match. I got the black screen into computer freeze.

Update I'm at my wits end on this problem so I'm done with league until this gets fixed. I'll try back in upcoming patches. I can't seem to replicate this problem in other games so it's safe to assume it's a league issue with all the current bugs they already have (I get the login bug too).