I would first try to reboot while holding down Command+Option+P+R. You will hear the startup "bong" two times. This will zap the PRAM, which could possibly solve your problem.
To zap the PRAM, you need to hold down those keys for a total of three startup chimes.
Maybe try booting into single user mode and running FSCK
This would help with a disk problem, but not with an improperly configured display problem.
To fix your resolution problem:
1) Restart into single user mode
- Restart while holding Command+S
- You'll see a whole bunch of text fly by
By default, your hard drive is mounted as read-only. To change this...
2) Type "/sbin/fsck -fy" (without the quotes)
- This will run a File System ChecK, -Force run, -answer Yes to all questions
3) That should report back something like "Macintosh HD is OK!" or whatever. If it doesn't say your hard drive is OK, then run the command again until it does. (However, because you don't have a disk problem, this is most likely just a formality before you can mount your hard drive)
Now that we've determined the hard drive is clean, let's mount it read/write
4) Type "/sbin/mount -wu /"
-This will Mount, -Write access, -Update the already mounted filesystem /
5) Figure out your short user name by typing "ls /Users/"; you'll need it in the next step.
- This will LiSt /Users/
- You'll see "Shared" and some number of other users. Choose the one that belongs to your account. If there's only one other one there, well, that makes it easy.
We want to delete the "com.apple.windowserver.XXXXXXX.plist" file, where the Xs represent your computer's hardware MAC address.
6) Type "rm /Users/<<<the short username from the step above>>>/Library/Preferences/ByHost/com.apple.w"<<<now, hit the tab key to autocomplete the rest of the file>>>
- This ought to fill in the rest of the line with the filename, if it doesn't, post here and I'll update the instructions accordingly
7) Type "shutdown -r now"
-This will Shutdown, -Restart type down, at time Now.