Hard Drive Size reduced and regained automatically

Hello!
While surfing the web, I got a notification that I'm running low on drive c. When I checked the drive it was just 75 MB free, while earlier it was around 7.05 GB free. After sometime, it changed to 5.32 GB free and then again to 7.05 GB free. What went wrong? Any serious problem? I was using Firefox browser and am on windows xp. Please help.
Thanks

 

windows works best with 15% to 20% percent free space.

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what is your current antivirus??

do the following to insure your pc is clean:

Download, install, update and do full scan with these free malware detection programs:

Malwarebytes Free (MBAM): http://www.malwarebytes.org/products/

SUPERAntiSpyware: (SAS): http://www.superantispyware.com/

Remove all found, reboot, and run again until scans run clean, these can be removed afterwards if you so choose. Run scans one at a time, please.
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remove any old system restore points by using disk cleanup, more options tab, click on clean up system restore this will eliminate all but the last system restore point cleaning up much space.

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download TFC from here:

http://www.bleepingcomputer.com/download/tfc/

and run it.

if you do not have ccleaner installed, then I would recommend that you install it. and run every day, just do not run the registry part, and check the listings to clean only what you want.

 

ALSO: you can check in event viewer at the time of the occurrence to see if an event was logged as a warning or error.