My Hard Disk Space Disappeared Mysteriously

Why oh why I do not know about this earlier? I watch in front of my eyes my hard disk space reducing all this while, without actually knowing the reason. Tonight, my hard disk is down to 120MB - and that is low for an operating hard disk - and I am really determined to find out the culprit. I keep blaming the virus, or the installed programmes (I even deleted some of them!) but to my dismay, my hard disk keeps shrinking. Luckily my pendrive, heavily infested with viruses from my friend's laptop, informed me, metaphorically speaking, that the Kaspersky I use for years needs more space to keep its backup files! It hangs while waiting for the cleansing, so I yank the pendrive, restart my laptop, and surf. I found this entry which helps me a lot. Now, smiling broadly, I will continue to clean my pendrive again. Oh, and thanks Mr. Google.