full disc bug or virus

My daughter has been using her new win 8 laptop for 2 months. Her C drive of 75 gb appears to be full (1.60 gb free), she can no longer download programs like the win 8.1 update. She regularly runs AVG free, spybot and ccleaner, nothing can be found. Optimising the drive made no difference. Reading up on-line there seem to be different opinions on the cause - a Win 8 bug, a virus. Are there simple steps we can take to at least find out the cause before we give it away to have it fixed? Can it be rescued?

Hello Happygreen,

To request assistance in this forum the FAQ includes guidelines in post #1 and instructions in post #2 on how to provide the preliminary DDS and aswMBR logs used for analysis.

http://forums.spybot.info/showthread.php?t=288

Then start a new topic providing the logs, a volunteer analyst will advise when available. :)

Best regards.