annie~when you say it is not cleanly cutting cardstock, is the blade making it all the way through the paper? Do you have it set at max pressure? Have you tried adjusting the blade depth?
You can surely call PC and I am sure they will be happy to help. I know for a while they had issues with the original blades being dull. Mine was fine, but you may also want to try a new blade.
Check out
www.cricut.com for their facts section that will answer common problems. They also have a message board.
HTH