Check for any viruses or spyware with the following programs if you havent got them
AVG ANYIVIRUS FREE EDITION (free.grisoft.com)
AVG ANTISPYWARE FREE (use above site.)
If you have already checked, go to my computer, control panel, system and check how much RAM you have. If it is an older PC you may want to consider upgrading the memory at click here and clicking Scan My Computer.