Computer Help

[CWsports]

I purchased a new hard drive about a week ago. I hooked up the old hard drive and an extra monitor and put that in a spare room. The other day I went to boot up in order to get my Poker Traker database files so I could move them to a new computer. The computer started up and after about 15 seconds it got to the desktop. Today I tried to boot up and the computer will start up and the monitor will have an HP screen in the background but for some reason the desktop doesn't come up. It looks like it is getting stuck and nothing happens. Any ideas as to what the problem is?