More often, the hard disk space becomes hogged and leaves an user to think what's the cause. If general, the following are the major consumers of hard disk space:
System Restore snapshots
Temporary Internet Files / History
You can free-up the space by running Disk Cleanup utility. Click Start, and then click Run. In the Open box, type cleanmgr, and then click OK. Select the drive, More Options, System Restore, Cleanup.
This purges all the restore points except the newest point. This should clear-up most of the disk space. If not, choose the following options disk cleanup and run it:
Remove temporary Internet files
Remove downloaded program files
Empty the Recycle Bin
Remove Windows temporary files
Description of the Disk Cleanup Tool | Automate Disk Cleanup using Task Scheduler
There may be other areas/folders which occupies your hard disk space and it's difficult [without a third-party utility] to track-down which folders are the major consumers. Windows Explorer / My Computer views shows the disk space data for the current working folder/drive only.
DISKdata is a powerful explorer-like application for Windows 95/98/ME/NT/2000/XP that analyzes disk space utilization. Selecting a disk volume or folder displays a summary of its contents in report or chart format. Using DiskDATA, you can drill-down each folder and generate charts & reports in CSV format. Here are the screen-shots
drill-down User Profiles => Pie-chart type =>
Download DiskDATA from http://www.digallery.com/diskdata/