MacBook Pro 2010 all of a sudden slow

So literally out of the blue, my MB Pro is giving me the rainbow for minutes at time for 99% of the things I try to do.

I maxed out the memory to 8GB last year, and that made a huge improvement, but like I said, this afternoon it went from being a really productive machine to acting like a 10-year old computer.

I'm thinking my hard drive is about to die considering I plugged in for a time machine backup and it says 14 hours for a 210GB backup. Is that right?

A solution would be great, but just knowing what could possibly be going on would be a relief as well.