limited Disk space
The first thing is to do a disk cleanup, you can do this by right clicking on the disk icon and selecting properties or use a one of the excellent downloads such as 'wise disk cleaner free'.
After that you have 2 options - do a file search on that drive for files over 2 Megabyte and then arrange them in order of file size this will tell you which files are taking up the most disk space so you can delete them or move them to an external drive. OR download a program called space monger (30 day trial will be long enough to sort out your problem) this has the option to be installed on a USB drive in case you do not have room on your hard drive, This will give you a more in depth view into what is going on with your hard drive and allow you to remove large unwanted files.
Once you have created space you will need to defrag your hard drive, again windows has a utility for this but I prefer to use the free prog 'UltimateDefrag' from DiskTrix.
If you are still having a problem then do a deep virus scan on your hard drive, I find one of the best free tools for the job is called 'SuperAntiSpyware'.