Random computer crashes and lockups could be caused by too little free hard drive space. Check drive C to make sure you have at least twenty percent or more free space available. If you do not have enough free space, either install another hard drive and move some information from drive C onto this or remove some programs and information to free up more space on C drive.
The most important computer repair safety tip to remember is that before servicing anything on your computer, be sure that you have the power turned off. Even if you are only going to remove the computer case to look inside, be sure you have the power turned off. Many personal computers have internal lights, so be sure they are not on once you turn the power off. If any of the lights remain on, the power is not completely turned off.