Assuming no hardware issue and you are running windows of some sort:
First: ASSUME YOU WILL OR ALREADY HAVE LOST ALL INFO. Find a local geek or tech and see if they'll back up your drive for you. Going forward, using the tools below, may (read that as Most definitely will) cause complete loss of data.
It sounds like you either don't have an operating system or the BIOS cannot find the operating system. Most likely the latter. Hopefully you have the original disks that came with the unit. .If you don't, you can order them from HP for about $5 plus shipping.
Depending on the version of windows, you might be able to get the restore disk from HP and just boot to the disk and fix it within a few minutes.
But it sounds to me like your master boot record isn't being recognized and would need to be repaired (ie, use the disk and repair it) before you can get back into the OS. This happened to me on an HP last year and it took me a couple hours with the disk to work out getting it back to working condition.