Rant time.
Some idiot was considerate but smug as he read about people with computer viruses.
And then he got his in triplicate!
Every once in a while I'll check my internet activity. Three days ago I noticed that it was a bit too active.
That was three days ago. 
Something had turned off my favorite antivirus Avast and set the firewall, Comodo, to let it all pass in and out.
Spoiler:
Other signs of a virus infection.
You have a problem when try to update your virus definitions.
You are unable to even connect to other antivirus web pages.
Very high hard disk activity
Slow computer.
Restated in Safe Mode, ran some online A/V (antivirus) programs. After detecting and removing 3 viruses my computer refused to boot.
Great.
In went the Windows 7 DVD and I did a repair. Boots, but bad logon.
Password straightened out with Trinity. Computer starts , and I can log on. Internet activity still too high.
I noticed that the updated A/V program stalls for about 2 minutes on a file that isn't all that large, and then goes on to completion.
Can't delete file, can't move it. Just simply can't do anything with it.
Restart for the 200th time (or was it 300th?) in Safe Mode and now I can delete all the files in the folder (along with the folder). I run CCleaner on the registry.
Can't connect to any A/V websites (or if I can connect in Safe Mode I can't run it in Safe Mode). I delete a bad "hosts" file.
I'm now able to download a new A/V program and run it. Delete that one, install another and run it. Restart Windows and download another A/V program, run that one too. Delete that one, install another one and run that.
The virus that caused the problem seems to be gone now. Hard disk & internet activity is back to normal.
The only problem is that so many infected files were removed that the computer is acting strange. DVD/CD is read only - all blank disks are tagged as full, Windows "Gadgets" no longer work, FireFox is unuseable, etc.
Luckily I can do a "Windows upgrade" from the origional DVD to restore the bad/missing files.
Everything is back to normal & I still have all my programs and documents.
Short story part.
Trinity Rescue Kit - Among other things can be used to reset Window passwords up to, and including, Window 7.
Repair Install - Windows 7
I know, I know. I should switch to Linux. Linux has no viruses.
I have to work in the real world. The people I do work for (universities, military, corporate 1000, etc.) use Windows in their day to day business.
Side rant.
It's amazing how many people have an unthinking, irrational hated of Microsoft.
When MS was working out of a house and small, everybody loved them. They got real big & everybody hates them.
Kids born in the last 20 - 30 years don't even think of it, they just hate "Big Business". Microsoft is "Big Business" and therefore bad.
The same thing would have happened if their product was Apple or Linux OS/software.
In fact it looks like Apple is getting big enough to draw that kind of knee jerk reaction too.
It's amazing how some really smart people can be so childish and stupid.