My apologies I think my instructions were a little lacking in regards to verboseness. Here they are again with some more explanation:
1. delete the contents of:
Mac hard drive/Users/[Your user name here]/Library/Cache
...it is OK to delete the whole contents of this folder, as it just stores things so they can be opened/used a bit more quickly. all the contents will be automatically recreated over time.
2. Go to this folder
Mac hard drive/Users/[Your user name here]/Library/Preferences/
Look for any reference to Scype. look in the filenames of all the files there. It will probably end in ".plist", but may not. (these are all your personal preference files, and can sometimes become corrupt. they also get recreated when you delete or change their name, but you'll loose some preferences each time you do this, so don't go deleting willy-nilly).
3.If you find a likely suspect, try renaming it by adding a few characters at the end of the filename (like "suspect-file.plist.OLD"), then try re-logging in.
If all the above doesn't work, try doing step 3 with the file "loginwindow.plist". If stuff stops working after you do this, simply rename your old loginwindow.plist file back (i.e. remove the ".OLD" at the end).
The ~ sign means start in your home directory.
4. try running the program as a different user. (create a new user in system preferences>accounts if you don't have a spare account lying round.)
5. There are also preference files in mac hdd/Library/Peferences that you might try backing up and removing, like the above.
try the above 5 steps carefully! don't forget to log in and out inbetween them. good luck!
keep me posted.