Can't log on to iMac.

I can't login into my account on my iMac. I am writing this from my iPad.

I first noticed some strange behavior on my iMac. Whenever I opened a folder, I could only access the top, or first appearing item in that folder. Whenever a field requiring an entry, such as User Name, appeared, the field would be automatically filled with a continuous string of the character "[". I could not delete the character string or enter anything into the field. I also noticed a unknown .doc document as the first listed item in my document folder. I deleted that document, thinking it might be the cause of the strange behavior. The behavior continued. I tried to restore to a previous time point using Time Machine, but I could only choose the top listed item in any chosen folder. I did a virus scan using ClamXAV. It found nothing. I tried booting in Safe Boot. The same thing happened.

The machine acts as if it has been infected with some piece of malware. Does anyone have any thoughts on how I could log in to my account and clear up whatever is wrong with my iMac?

Frank Bendrick