Frequent Bsdos On Number Of Different Error Codes

I've been suffering more or less frequent BSODs for a while. They usually come when I'm playing something, ranging from Orcs Must Die to Fallout 3. Most often they appear when I'm on Skype, chatting with people while playing Magicka or League of Legends. These BSODs are often accompanied with loud, "buzzing" sound which disappears only after the computer reboots itself. There have been many kinds of files which seem to be the cause behind the crash such as win32k.sys, dxgmms1.sys, nvlddmkm.sys, usbohci.sys and so on, but I don't know what to do about them.I've updated my GFX, chipset and soundboard (I think, it's integrated) drivers and flashed the BIOS. I've also reinstalled the OS once, few months ago I guess. I've checked RAM with memtest, turned out fine, same with hard drives. I haven't monitored computer temps very closely, but I have removed the side of the case so the air should be flowing freely. The crashes are also quite random.