I have several movies/tv series/music files on my pc. they are randomly being deleted. Or possibly hidden. Music files are gone from the hd but still show up in playlises (won't play) and movies still take up space on the HD but can't be found in their folders or by search. Folders with many files still say they have the original amount of files. Ie. a folder with 15 tracks in it now only has 13 but if I check properties it tells me 15 files are still present. WTF is going on?
Have you tried running check disk? Right click on the properties on the drive icon, select tools and click on check now. If you can’t get it to do the three phases try from the DOS prompt. With this sort of problem a virus is of course a suspect try a free copy of malwarebytes anti virus.
I had this happen to me just a few days ago with an external harddrive. In my case, I moved 280 photos (2GB) from my camera to an external harddrive (I was away from home on holiday) and all 280 files disappeared suddenly when I was looking through them. It wasn't until I got home, took the external hdd out of its case, put it in my computer (I hate externals), and fiddled a bit that I found all the files were perfectly in tact.
The cause for this and your scenario can be most accounted to corruption of the MFT. As the Master File Table (MFT) contains all the information of where your files are on the disk (ie. what sectors they start and finish in), any corruption of MFT entries will screw with what the computer sees on the drive. For instance, if you delete/clear the MFT (this is what a quick format does), all the data is still physically on the drive, it is just not indexed (the computer will see it as free space).
In my case, I think the corruption of the MFT was due to the drive stopping responding indefinitely and me unplugging it (it has a super shitty USB-SATA controller). Windows XP would say "Delayed write failure" and detail that it could not write to the MFT. My guess is that after doing this several times, things got messed up and the entry for my 280 photos was damaged (along with the drive header as the drive soon became unusable!). Also, I am aware that this drive has quite a few bad sectors (probably for the same reason - I HATE EXTERNALS) and this could have added to MFT corruption.
[Just thought I'd put this in for extra info] Bad sectors are sectors (physical areas) of a harddrive that have been damaged permanently. Any data that was contained in a sector-gone-bad is unrecoverable, and thus any file that spans a damaged sector (potentially) becomes corrupt as part of it is gone. When a computer 'fixes' bad sectors, it records the location and essentially writes an instruction to skip over that sector in future to prevent further loss of data by writing a new file across an unwritable sector.
Windows XP (what my laptop is running) seems to have problems dealing with bad sectors and MFT corruption, and it took my Windows 7 desktop computer to repair the damage (probably caused by XP to start with). As you have posted this is the Windows 7 forum though, I assume you are running windows 7?
Getting to instructions:
To check for bad sectors and MFT issues, in a command prompt (click start, type cmd and press enter) change to the drive in question by typing the drive letter and a colon (d: or e: or f: etc) and pressing enter. Now type chkdsk and press enter. Wait for this to finish (you'll see your drive letter again), then copy the output and paste into your reply here (to copy, rightclick -> select all and press enter). Should look something like this:
Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.
The type of the file system is NTFS.
Volume label is Programs.
WARNING! F parameter not specified.
Running CHKDSK in read-only mode.
CHKDSK is verifying files (stage 1 of 3)...
30976 file records processed.
File verification completed.
1 large file records processed.
0 bad file records processed.
0 EA records processed.
0 reparse records processed.
CHKDSK is verifying indexes (stage 2 of 3)...
33892 index entries processed.
Index verification completed.
0 unindexed files scanned.
0 unindexed files recovered.
CHKDSK is verifying security descriptors (stage 3 of 3)...
30976 file SDs/SIDs processed.
Security descriptor verification completed.
1459 data files processed.
CHKDSK is verifying Usn Journal...
8540832 USN bytes processed.
Usn Journal verification completed.
Windows has checked the file system and found no problems.
102396927 KB total disk space.
66757236 KB in 28297 files.
12780 KB in 1460 indexes.
0 KB in bad sectors.
108807 KB in use by the system.
65536 KB occupied by the log file.
35518104 KB available on disk.
4096 bytes in each allocation unit.
25599231 total allocation units on disk.
8879526 allocation units available on disk.
Unable to obtain a handle to the event log.
I'll be able to give you a definitive answer after I see the chkdsk result, but my thoughts now are that you should backup your files as soon as possible to prevent further loss - it is possible your drive is failing due to many bad sectors. BUT DO NOT PANICK! It is possible that some MFT entries are damaged but the disk is healthy (this is repairable).
Just another note - damaged MFT entries can cause files to disappear, but the way the MFT works, folders can still register as their full size even with damaged entries (the computer might see there is a file that is xxxx bytes, so the file is counted for size on disk, but part of the entry is damaged so when the computer goes to display it, it fails).
pjmelect has a point, do you have a virus scanner installed?
It's likely that virus may turns the files and folders into hidden files, or shortcut files, you may try to show hidden them, see this guide: http://goo.gl/6Ees1L
Since the files takes the space, so do not need to be too worried, it's likely that the files are still on the hard drive, you may scan your computer with microsoft security essential http://goo.gl/w9nHt
After the virus is killed, the files should be back.