This seems to be common for some reason when trying to run Windows 7 under KVM and 7 has always had strange issues with KVM. What happens for me is after the install it simply won't boot, it stays on the POST screen and does nothing.
For some reason it appears the boot sector either doesn't get installed or gets corrupted with KVM.
The solution is to boot the install disc for Windows 7 and reinstall the windows MBR into the boot sector:
1. Boot t........