Macbook pro 13" problems

I have a macbook pro 13" core i7 machine that i'm experiencing problems with.
Sometimes when I turn on the machine the apple logo (loading) screen seems to freeze and won't move on to the log in screen, other times it boots just fine.
Also sometimes when I have been using the machine for half an hour or more using various programs such as chrome, safari, iphoto it freezes and I have to manually shut it down, following this I go through a rigmarole of freezing and rebooting several times.

I verified the disk in utilities and it did a small repair, but didn't find any other problems. :S

any advice or insight would be appreciated.

The hard drive may still be having problems even after Disk Utility did a repair. The problem with Disk Utility is that it only repairs such things as files, folders, and other types of disk errors. It can't accurately detect hardware problems. For that you need to run the S.M.A.R.T. utility.

Download from here.

thanks very much for your help!
downloaded smart utility and as predicted unfortunately the overall diagnosis was hard drive failing.
glad to have it narrowed it down to one thing so I can get it sorted.

Thanks again