I quarantined a file using AVG. then I deleted all files of AVG (Including Quarantine information),
By booting from Windows Live CD.
Now , although that file is present on my hard disk, it is unusable. How can I get it back?

Maybe you can search for the file -- then overwrite the bad file

Top 100 Shareware downloads at SnapFiles

File Scavenger is a Windows file undelete and data recovery utility for NTFS and

FAT/FAT32 volumes. It can recover files that were damaged by virus...

There are 2 ways that viruses get into useful files:

1) Intentionally. Hackers take highly desirable files (hot movies, expensive software) and embed a virus inside, and then upload the file to a file sharing site or service. Dump the file, and get a good copy, preferably from a legitimate source. It is much too risky to try to clean the file and use it - it may have another as-yet undiscovered virus still inside. You don't want to be Hackee Zero for a new virus that deletes all your important files, do you?

2) Accidentally. A friend or co-worker has a virus infected system and it infected a file that they sent on to you. Have them clean their system, then resend you a clean file.

Jc