Windows Is Showing Wrong Disk Space In C Drive?

I have one more problem with my laptop this time . i have a Dell xps 15 , i re partitioned it and made my C drive of 141 GB . i installed all the required application and from the last few days i was watching the there is less space in my C drive than it should be there. i checked out the properties and found out that only 32.6 GB of disk space is utilized out of 141 so there should be around 108 GB free instead it shows me that only 92.9 gb is free .i cleared out the temp folder and there is nothing except 3-4 files which is of some Kbs . then where is the rest 15 GB gone ? is there a virus in my pc which is eating up the space ? i am really freaked out

i have a genuine windows 7 ultimate and microsoft security essential and it is updated and i scanned it and found nothing . btw there is something more , few hours ago there was 94.8 GB free , i installed a game in another drive and i removed it after 2-3 minutes coz i didn't liked it , so after un installing the game i saw there there was 93.4 GB left in my c drive again , i removed files from the temp folder but nothing happened and now there is just 92.9 gb left ! what is happening ! i am really freaked out now