Boris: Glad you're system is running better. You got some really good advice so far.
It appears you have a corrupted Windows7 OS at this point. Reference this information on the Windows Media Player 12:
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Windows Media Player 12 (WMP12) is the default and factory-installed media player that comes with Windows 7, and WMP12 does not have standalone setup installer available for free download. As such,
Windows 7 users cannot uninstall and install Windows Media Player 12 manually. In fact, there is no entry of WMP12 in “Programs and Features” that allows uninstallation or removal.
There is chance that user may need to uninstall, remove and then re-
install Windows Media Player 12, such as to fix WMP corruption (possibly due to attempt to
downgrade or convert WMP12 to WMP11), or to reset and re-configure Windows Media Player.
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I verified this information by trying to download the standalone WMP12 installer from several different sites, and they always take you back to Microsoft's download site for WMP12.
If your computer is working ok on the Internet and Email and other basic functions, you may have to learn to live with the WMP12 error. If you cannot, your options include repairing Windows7 from the Recovery Console accessible via the F8 key on computer startup. This usually only works in 30% of the attempts from what I've seen.
Since you've got an integral component of Win7 which has been embedded in the OS kernel; much as has been done with Internet Explorer recent versions, the Windows Recovery Console doesn't have the ability to repair a busted OS kernel. It can only repair missing or corrupted files; but the OS kernel is compiled code, and you can't fix that with that tool.
The repair basically would consist of running the Factore System Image Recovery program either from discs that came with your Dell (you didn't mention whether you had a desktop or laptop), or run from the built-in Recovery Partition on your hard drive. Depending on the model of your Dell, you may be able to access that program from within Windows via a Dell utility that came with your computer called Dell DataSafe. If you don't have that program on your model Dell, you will have to use the Windows Recovery Console (F8 key) to access it. I suggest at this point you backup all of your Critical Data to external Hard Drive, Flash Drive, or CD/DVD discs. Then run the Factory Partition Repair to restore your computer to what we call "Out-of-Box' condition; or the condition the computer came in when you first opened it when brand new sealed in the box.
Ensure you select the
FORMAT DRIVE option to remove any Malware or RootKits which are known to hide in the Recovery Partition files as well. (Yes, I've run into this recently on Customer computers).
This will correct your problem, and since WMP12 is built into most Windows7 versions, it will now work without giving your nagging error messages!
However, if you have one of the versions of Windows7 that doesn't support built-in WMP; you'll have to download via the microsoft.com website. So, for example if you have Win7 RT; you'll have to go through the download to get the WMP12 player.
If you are not using WMP player, and just wanted to eliminate the error message, my suggestions above will fix your problem.
After you get all working again, make sure to install one of the Anti-Malware programs and use the MBAM as suggested for manual scans. There are a number of viruses out there that attack the WMP just like there are many programs written to attack Internet Explorer. As I said earlier, since both are built into the OS kernel of Windows, hackers love to write viruses to attack vulnerable Windows systems that have no, expired, or out of date anti-virus anti-malware software such as your system appeared to have. Attack your Windows Kernel and your Windows is compromised and never works right, which was the Hacker's goal who wrote the virus you got infected with on your system.
Hope that helps...
BIGBEARJEDI