Problem loading OS

I finally got my new computer to work, and i used Partition Magic 8 to partition the hard drive to make it so i could install another OS. Well, it did all that, and i restarted the computer. And now when i put in an OS disk the computer won't read the disk. I have it so it reads the disk first, but it stops reading the disks. I tried using 3 different OS's, and i'm positive it's not the disks. I'm not sure what the problem is with the computer, i've been having lots of problems with it, than i finally got it to work, but now i'm having this problem. So if there is anyone that can please help me, and not ask if i checked all my cables or something, that would be lots of help.

Thanks