I had the same issue and I fixed it last night.
Here is what I did to correct it on my system:
1) Go into BIOS by immediately pressing delete when the system is first turning on and ensure that your hard drive is recognized, if it is, then set boot order to first boot from CDROM instead of the hard disk and save that setting
2) Insert your Windows 7 disk
3) Restart Computer (should be booting from Win 7 Disk now)
4) When you get to the first screen of the Win 7 install, press SHIFT + F10 to open the command prompt
5) In CP type diskpart then hit enter
6) Now type list disk and hit enter
7) If you only have 1 hard drive it should say "Disk 0" and info about the disk (size, free space, etc)
8) Type select disk 0 and hit enter
9) You should now see a line that says "Disk 0 is now selected" or something to that effect
10) Now type clear and hit enter (this is removing any partitions that might have been present, like a hard drive reset I guess)
11) Type list disk again and your hard drive size and hard drive free space should now be the same
12) Type exit hit enter and then type exit and hit enter again
13) Cancel the Win 7 install and restart you system (still booting from the CDROM and the Win 7 disk) and you should be able to get all the way through the installation process
It turns out that, in my case, I had accidentally partitioned 100% of my hard drive so there was nowhere to install Win 7. After I did this it was smooth sailing. You could be getting the same "Loading Operation System" stall because of another issue but this was how I got past it.