you can follow the link...
http://www.thinkdigit.com/forum/viewtopic.php?t=16885
alternately my post is repeated here
the space has probably been taken up by
1. swap file (pagefile.sys)
2. Old System restore Files
3. Old chkdsk files
4. and if you have hibernate option enabled ..then it used some space too (hiberfil.sys)
To create space ...
1. you can move swap file elswhere on your HDD
2. Disable system restore or delete old restore points..
3. run disk cleanup to remove temp files and old chkdsk files.
4. disable hibernate option and delete the above file(hiberfil.sys) manually if it is not automatically deleted..
Hope your querry is solved..
Hitesh Gupta