I never had any problem with the capacity of my hard disk (±300GB) until I installed Sims 3 on my laptop. It took up about 5GB on the C drive but immediately the bar showing the free space on the disk drive turns red. Hmm... I thought I had a lot of free space. Definitely more than 20GB.
Then I started deleting my old files and all the programs that I seldom used like all the little games. But they took up so little space that their extermination didn't do much difference. I was freaked out when the free space kept getting smaller despite all my efforts and I had to do all those disk cleanup operations every now and then. I continued deleting files or transferring them to the other drives (strangely, only the C drive was affected) but it was no use. I finally uninstall Sims 3 (so long, Ms. Black!). Though not very much, it freed up almost 6GB.
But not for long. The free space dwindled to about 400MB is less than 2 days when I didn't do anything at all that might gobble up that much space. I panicked (O_O)
I did everything I could using Avira AntiVir that I was using at the time but it detected nothing. And it was up-to-date too. The message 'You have little free space' or something like that kept popping out from the taskbar. Then I decided to switch to AVG. Of course it is wiser to just buy a good, reliable antivirus but as far as my family is concerned, we never buy one when the free downloaded versions are good enough. And they were, up till then.
After all the procedures of installing and running the first scan was done, there were 46GB of free space in C! Woohoo! Problem solved! Why didn't I think of that in the first place? Instead I have to uninstall a lot of programs and other stuff. Aiyo... Lesson learnt. Maybe I'll consider buying Karpersky Antivirus like my brother asked me to.