Isass.exe error - I can't even log into XP! Help please!

I need some help please! I have an XP OS and I can't even log on. It
appears to try to boot up, but it just keeps going in circles, doing the same
thing. I get one error that says: Isass.exe System Error Insufficient
system resources exist to complete the API. Can any one of you geniuses help
me...I really need it! Thank you so much! I am not sure where to post this
question, so if it is wrong, I apologize.

Jean