I recently had some serious problems with Windows 7. The outward sign was that all the transparency effects were no longer working. The more serious issue was that Chrome, IE8 and IE9 became unusable for browsing web pages. Firefox worked a bit better but, things still weren't working well. I restored my system from a backup and most everything worked well after I booted from my Win7 disk and ran some repairs to fix the master boot record.
One thing that didn't work was the terminal emulator I use for embedded troubleshooting. Launching it caused me to get an immediate error dialog telling me I was missing msvcr71.dll. From the name I was pretty sure it was a microsoft visual C library. A quick search of my system turned up dozens of copies of this .dll. The question was where did my terminal emulator want it to be. A quick google search led me to a page with the answer: the C:\Windows\SysWOW64 directory. The link provides downloads of the .dll but I would suggest you look on your own system so see if you already have a copy you can use. Downloading .dll's from web sites you don't completely trust can be dangerous.