Random Screen freezes,

Ok so here it is, i have made a few other threads about this issue but none seem to resolve it.

I keep getting random screen freezes where my mouse and keyboard lockup and so does the screen. im not really sure what causes this but it happens at different times, it could happen when i run a program or using one, it could happen a few minutes after everything has loaded it sometimes happens when the logon screen comes up saying "Welcome".

I tried a clean install of windows but still the problem is there????

HELP!!

P.S i have a pc that was built from differnt parts it is not a company pc i.e dell, asus, toshiba...

Oh wait i think i have fixed it i simply increased the RAM Voltage up to 1.60 and it seems to be running fine. ill post again if it happens.