so today my computer was crashing basically everything was not responding on screen so i hit restart pc. when it restarted it wouldn't boot up or anything, (fans powered on thats about it).I unplugged it checked everything inside the case ( its very dusty i blew as much out with my mouth as i could) but doesn't seem to be anything out of place. I managed to get the computer to start and bios loaded and i hit f2 to load with default values and it went to a black screen saying checking nvram and basically stopped there for an hour.I managed to boot the pc now by going to setup and clicking load with default values. any idea what caused this? can i prevent this from happening again? any easy way to fix this if it does happen again? also running window 7 64 bit.