HFS Partition disappear from Mac OSX [PLEASE HELP]

[peterpan0215]

-----Background-----
          I have a Late 2011 MacBook Pro with both Mac OSX and Windows7 installed. I have two drives. One SSD (with two partition): Windows7 and OSX and one normal 700GB HDD (also with two partitions) that stores "Applications" and "User" information for OSX and "Program Files" for Windows 7 (to decrease space consumption on the SSD).

-----Problem-----
          After installing Avast Anti-Virus software on the Windows7, I started to do a "Full System Scan." The Full System Scan took the whole night and was only at 20%, so I stopped the scan (I suspect it was because the two HFS partition on the SSD and HDD). After stopping the system scan I wanted to switch back to OSX but was unable to log into the user's account. I went into the guest account and found out that all applications are gone and was unable to locate the HDD's HFS partition when trying to locate it in "Finder" (which is probably why OSX was unable to log in and also unable to locate applications). However, I was able to see the OSX partition on the SSD, Windows7 partition and even the Windows7 NTFS partition on the HDD but not the HFS partition on the HDD. I switch backed to Windows7 and was still able to see every partition including the HDD's HFS partition along with the user's information and applications for OSX.

-----Question-----
          I'm quite positive that it was caused by Avast because the OSX was completely normal right before I downloaded Avast and did the system scan. Or could it be something else? The questions now is what I should do to allow the OSX to once again find the HFS partition on the HDD. I can't open any applications on guest in OSX so I can't do "Time Machine" or even "Disk Utility." I could possibly restore from my time machine back up from my external 2TB HDD but that would mean I have to re install Windows and everything again so this solution would be my last option. Because I can still see the HFS HDD partition when I am in Windows7, I assume there is a way to let OSX re-recognize the drive and get back my user information and applications to allow proper OSX boot. Has anyone else encounter a similar problem? Any ideas on what caused the problem and what would be a possible solution? Any help is appreciate. Sorry for the long post. Really frustrated at the moment  Thank you!

[peterpan0215]

          I've found out the cause of this: the Mac's HDD were formatted from HFS to FAT therefore, I was able to access it via Windows but not through Mac OSX boot. I tried to repair the volume using Disk Utility but that didn't work out. Using time machine to restore the Mac partition didn't work too probably because the partition is in a different format. So I've decided to back up the whole Mac's HDD partition into a 2TB external HD, format the Mac's partition, then transfer the file back into the Mac's partition using MacDrive. Dunno if it'll work but I'm giving it a try.

Avast! should not automatically format a drive from HFS to FAT just so it could scan it for virus. Even if it does, at least have a warning message to alert the user. Please fix this issue for future users that might also run into the same problem.

[mity]

First of all, you are in the forum for avast! for Mac OS X, but your report is about avast! for Windows. Forum about that product is here:
http://forum.avast.com/index.php?board=2.0
 
Second, although I am in the avast! for Mac team and I am not too familiar with the Windows product, I really very strongly believe avast! for Windows never formats any volumes. I think, you should search the culprit elsewhere.

Best regards,
Mity