Macbook Pro power up problem

I have a Macbook Pro which does not power up correctly.

The startup screen appears and remains indefinitely after login.

Safe Mode cannot be entered.

Is there another key combination that can be used to enter another diagnostic mode?

I suspect a virus, but it seems like it could also be a memory or hard drive issue.

btw, this was posted from an iMac, so the form wopuld not allow me to identify the product as Macbook Pro.

The "Add or edit my products" link jumps to another page and starts a new discussion.

Kind of frustrating.