Try making sure that nothing is loose inside. Also, if you have any spare parts, try swapping things in and out to rule stuff out. Otherwise you may need to take it to a repair shop or somewhere they would have enough spare parts to diagnose the problem.
Originally Posted by MadDog
Nope. Some computers need pairs of RAM to work.
Not true at all, you can easily run with 1 stick of RAM. It won't run as fast as before, but it will run.