Please Help "Service not started" error

Every time i boot my computer i get a small box that says Error,
service not started" the only box to hit is "OK" i click that and it
comes up a second time , click 'ok' again and boot up finishes.

I don't know why this started, it has been going on for about a week
now. i can't think of any changes i might have made that woudl cause
this.

any ideas?

thanks,
Mike