First thing that comes to my mind is the hard drive overheating. Check to see if the fan around the intake of the computer (front-most fan, usually right in front of the hard drive) is spinning. If not, it could have become disconnected from the power, or just be dusty; verify the connections or get some compressed air and blow down your entire system. (Note: Check the fan while the computer is running and troubleshoot while it is offline.)
If it's not dusty, and the fan isn't spinning, or it's spinning slow, you can either take the fan off, buy a new (matching) fan and replace it yourself, or give a tech-savvy friend of yours $10 to replace it for you (as opposed to taking it to GeekSquad and paying $30 to $70).
Next---since you say your computer is shared, check that it's not a computer virus. Verify your antivirus software is up to date (and if you don't have any, you can get good software for free here
) and do a full system scan.
If neither of those things are the problem, check the things I mentioned for the laptop; CHKDSK, SFC and Defrag.
Let me know which one of those options seems to work. If none of them work, I'll need some more information about the system (operating system, RAM, processor speed, hard drive capacity and free space, and how much virtual memory is currently allotted). Also, regarding Virtual Memory, you should verify that you have at least 100% of your memory allocated as virtual memory on your primary or secondary hard drive (if applicable; secondary is preferred). That should significantly improve overall performance.