This is another one I hope no one ever experiences, but just in case, here's the info to file away in your knowledge banks...
Had a Very seldom used DVD re-writer in my wife's PC -- stuck it in new a few years back & never gave it a 2nd thought. Well, her PC has been getting slower, especially starting & shutting down Windows, but it finally got intolerable yesterday. Removed the drive, & everything's back to normal.
I hadn't known that a bad DVD drive could do that -- I diagnosed it sort of by accident. I connected a USB 3 hard drive, and when it didn't show up in Windows Explorer, I went to Control Panel -> Admin Tools -> Computer Mgmt. to assign it a drive letter. That part of the app wouldn't start -- couldn't connect to the vdisk service. That can be a bad drive, so disabled the DVD drive in Device Mgr. -- figured I'd start with the easiest -- and the Computer Mgmt. app worked just fine. SO bye bye to the DVD drive, & all was well.
