The memory in your computer is the working space for everything that it does. If your memory is having a problem, just about anything can happen - lock-ups, random error messages, lost files, startup problems... I could go on and on.
Lucky for us, there are some very powerful and completely free memory testing tools that anyone can use. Believe it or not, it's basically the same diagnostic software that nearly every computer-fix-it store uses.
Even if you have no use for it right now, it would be very wise to keep one of these memory tests in your arsenal of tools.