iMac is slow and freezes, all of a sudden?

Hi,

I have had my iMac (1TB) for 3months now and downloaded Mountain Lion on the first day of release.

I was using Photoshop Elements 10 yesterday when my iMac decided to freeze on me when trying to print off photos. I restarted the iMac, but since then the computer has been so slow and has frozen several times on me. I definitely have enough room on the startup disks, as I have managed to check that. I tried to run disk utility and verify the disks but it froze on me once again.

I get the coloured rainbow wheel quite frequently too.

I love my iMac and I use it frequently, has anybody experienced the same problem and what did you do to solve the problem?

Much help is needed, thanks.