VPS expert required - restore backup in whm

I'm having problems with my virtual private server. Up until the last couple of days it's been working perfectly however for some unkown reason I can no longer log in to WHM. I think the server needs to be rebuilt and restored from a backup. Rebuilidng the server can be done with teh click of a button in my HeartInternet dashboard however, I'm not sure how to restore the backup.

I need someone who has experience of managing a vps with good Linux command line knowledge.