f12, f8, delete, f2... theres several different ones. It *should* tell you while its posting (power on self test), which takes place before you see the Windows processes. If it does not show you, some tricks would be to press the TAB button (repeatedly) during the POST (may not have to do this). Perhaps there are other recovery options such as a hidden partition, I'm not there to verify (more systems these days have a built-in recovery function).
If verifying BIOS boot priority is correct (to boot from your hard drive first, then your drive has been damaged. If its software related, then all you need is to get your operating system repaired (full install of an operating system), or spend some time hair pulling via troubleshooting methods, or, recover from a previous backup (assuming you practice this - lesson learned!).
Its not all this easy obviously. You'll lose your data, which the majority of the time is what people care about, not the operating system. In the future, you would not want to store anything important to you on your operating system drive. A good example of why, is what you are currently experiencing. In the case you had made a system backup, you would be up in a matter of 10 minutes as all you would do is right click a file from your storage drive, and click recover (if you have the software to do this). No hair pulling, nobody to call for help (and pay). Assuming you have a storage drive, losing your OS is a tiny issue as all you'd do for repair is replace the drive (if hardware issue), or recover from a previous backup (if software issue).
