My acer extensa 5630z just randomly shuts off how do I fix this

try uninstalling a few unnecessary programs then click start run type cmd then type chkdsk/r/f which will scan for and attempt to fix any bad sectors and automatically fix any corrupt files on your hard drive this will schedule on a restart then defragment your hard drive

a possible reason could be a memory dump you might be running to many programs at the one time placing to much strain on the CPU also you might not have enough ram random acess memory to check what is running when your computer is running scroll to the bottom toolbar right click select task manager applications and processes if you see something you dont need running select end now to check how much ram you have click start right click om my computer select properties you will see all of your computers details

hope this helps