yesterday i did a system defragmentation and i was able to get 20Gb free now i only have 10Gb free and i didn't install any programs. can anyone help? thanks.

I don't know why 10G went adrift but defrag does not free anything. It simply compacts whatever you have, but the free space count remains unchanged. My guess is that it was due to some quite unrelated issue. some other bloke...

See drive properties. There should be disk clean up. Try that. Might have to look for orphaned files too. "Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10

In Vista System Restore will Take gigabytes of free space. When doing a clean-up select the option to delete system restore points up to the last one made. This will also recover lost space. There is no such thing as Health Food... just Health Fanatics!

Defrag will not create any new space; it only makes file contiguous to speed up access. If you have fluctuating disk space, it could be due to the page file or system restore points. There are some weird issues with defrag and system restore in Vista. A defragmenter such as Diskeeper 2009 with the ability to work around the volume shadow copy service is advisable if you want to prevent potential deletion of older system restore points. See this link for more info: http://www.diskeeperblog.com/archiv... I am not sure if this is indeed your problem since you seem to be losing space *after* you've finished defragging, which leads to me think that it's just system restore points being created 'normally' by Vista. Nothing to worry about.