Problem report for finder: finder quit unexpectedly

Question

Last night I removed some viruses etc., from my computer that were making ads appear and also tabs opening when not wanted by random ads. I then installed virus protection, and also installed a software update. During those processes I restarted my computer a few times. The last time, finder wouldn't close down but in the end my macbook restarted and since then I have this message constantly popping up: problem report for finder - finder quit unexpectedly. I can't open up anything else and get a message saying when I try: check with developer to make sure safari (as an example) works with this version of OS X. You may need to reinstall the application.
In ten the details part it states crashed thread 0 but it also mention application specific information:
dyld: launch, loading dependant libraries, ignoring DYLD_*env vars
and then:
dyld error message:
library not loaded:/ system/library/frameworks/videotoolbox.framework/versions/a/videotoolbox
referenced from: /system/library/frameworks/qtkit.framework/versions/a/qtkit
reason: image not found.
Please please help. It's driving me nuts. I really need my computer. So much that Im even contemplating just buying a new one if nothing works :/

Answer 1

FIrst, get rid of your "virus protection," which is either useless or worse than useless. Then see below.
If you don't already have a current backup, back up all data, then reinstall the OS.* You don't need to erase the startup volume, and you won't need the backup unless something goes wrong. If the system was upgraded from an older version of OS X, you may need the Apple ID and password you used.
If you use FileVault 2, then before running the Installer you must launch Disk Utility and select the icon of the FileVault startup volume ("Macintosh HD," unless you gave it a different name.) It will be nested below another icon with the same name. Click the Unlock button in the toolbar and enter your login password when prompted. Then quit Disk Utility to be returned to the main Recovery screen.
There are ways to back up a computer that isn't fully functional. Ask if you need guidance.
If you installed the Java runtime distributed by Apple and still need it, you'll have to reinstall it. The same goes for Xcode. All other data will be preserved.
*The linked support article refers to OS X 10.9 ("Mavericks"), but the procedure is the same for OS X 10.7 ("Lion") and later.