Check if you have emptied the recycle bin.
There are settings for the amount of space this can use, same for your browser's workspace. Either could be be too high.
Disc cleanup in programs/accessories./system tools may help as it scans and reports first what might be deleted. Takes a while to run though.
However far more information can be obtained from a free disk analyser, which can be downloaded.
e.g On my pc, one of these analysers showed Norton Internet Security was using a huge amount of diskspace, which never seemed reduce. Transpired it had a fault and was appending (rather than overwriting ) its downloads. Re-installing NIS cured.
Please advise back on progress.
Good Luck - Keep us posted.