T42 hard disk space

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I have a T42 2378FVU and have this tyipcal problem with the hdd. If I use the computer for a long time, the hdd space seems to be falling, and after like few hours, it starts giving warnings like disk space critical etc. I am not downloading anything and when i restart my system afresh the free disk space is close to 13-14 gb.

I have a hunch that the problem might be due to rapid restore/system restore or something. The problem intensifies if i hibernate a few times.

Anybody else had this problem? Possible solutions?