Ok when your computer "crashes" what that means is that your system locks up and is unusale or you get a "blue screen of death" (in windows). This is never something that you want to do or cause.
If you are running windows and u have high-speed internet i would suggest going to
http://www.trendmicro.comUse their free virus scan and removal tool. It will ask u to download an appication. run that on your machine and it will look for viruses and spyware etc. It will remove them for u as well and it of course it is free.
After that you\'ll know your machine is clean and should be in good shape. If the machine is still slow after that we can take a look at waht you have running on the machine and whats hogging system resources