Networks

Try using Treesize to determine what's taking up so much space.

http://www.snapfiles.com/get/treesize.html

I'm assuming you are using Windows Server?

First, search the c: drive for all files with files sizes above 10000KB. Be carefull of what you delete, but you may find installers and such that are taking up space.

Then, run disk cleanup, located under the system tools.

Last, you can look in the WINNT dir for files starting with $NtUninstall. These are the uninstallers for patches that are installed on your system. Once I install and test a patch, I then remove these files (they are hidden).
Example file name: $NtUninstallKB899589$

Hope this helps!

Check your recycle bin properties also as the OS automatically reserves whatever size is set.

maybe its because your computer's updates & patches. look into the windows\temp and look for the folder "OHotfix". You can delete the whole folder.

if you have turned on 'view all hidden and system files and folders' in Folder Options then you will see those hidden update folders (which I move btw, and don't delete, just lazy i guess). you can see how to move them at support.microsoft.com search hard drive space under your os which you did not mention...
anyhow if you can't see any hidden folders, you might have:
file system corruption (run chkdsk c: /f)
or some viuirii cause this, you could search for this as a symptom at support.symantec.com
you need to address this for sure. you are getting low enuf to have problems. i bet it's not a virus or you'd be down by now...
check the event logs always...