Right Click on the Start bar, and then click on My Computer.
You will have a disk on the right side which says Local drive, Right click on that and go to properties.
That will tell you how much disk space is currently used, and how much spare, it may give you an idea of whethert he computer is wrong, or you have too much stuff.
Do you have a lot of Photos?
Or music downloads?
What size is your hard drive? if you add the free space and used space it will give you your answer.