a. What is the make and model of your computer? <--- Built it my self 2 years ago, like I've built every PC I've owned since the early 90's. Never had any issues with XP, avoided Vista because the beta was atrocious and the release was worse. Beta'd 7 ran great, was very enthusiastic and pre-ordered Ultimate as soon as it was available. Beta ran flawless, but then again I didn't run WMP much. Looking back I probably should have....
b. Was the Windows 7 install an upgrade or a custom install? <--- Clean install off the retail 64 bit 7 Ultimate disk.
1. You may try performing a clean boot to check if there are any background programs that may be interfering. <--- Done this, same results. Also see original post about scanning PC for malware/viruses. I like a clean PC, I'm all performance based. No ____ in my tray that doesn't have to be there. Zonealarm, Avast, Malwarebytes, and APC's UPS software.
If the issue persists, you may verify that the proper codecs to play the video files are installed on the PC. <--- Again, please read above posts. I've already checked codecs. I also downloaded the K-lite codec pack, which has helped some, but only because some of the codecs contained are more forgiving playing MP3 files that are partially corrupted. * Edit - Note my MP3 files were NOT corrupt prior to trying to play them in WMP. K-lite only helps play some of these songs that WMP has damaged. After copying over fresh versions of the files from my backup drive, WMP will work fine, until it decides to corrupt them again. I've never seen a faulty codec corrupt a file. WMP that opens and edits the header file of MP3's so it can add it to the library... It's this procedure that has caused problems in the past, see above post, and is most likely causing issues again.
You may also create another user account and check if the issue occurs. <---I'll try it, but it sounds more like a stall tactic than a troubleshooting procedure. In 15 years of repairing PC's from Windows 3.11 on up, I have yet to see a corrupt user profile account for eating MP3 files and nothing else.......