I have a Pavilion p6347c with Windows 7 and had the same problem. Here's what I did to launch Windows:
1. Control-Alt-Delete
2. When system reboots, hit the ESC key and it will display the available drives.
3. With your up/down arrow select the first disc (has a bunch of letters and number)
4. Hit return and you should be able to launch Windows.
Still haven't figured out how this can be fixed, because I have to do this every time I restart my computer. Something to do with the BIOS. If someone knows the answer, please advise. Thanks.