Since you did not list the model number or the OS, this is a generic answer. Some or all of it might help you.
First thing is to run diagnostic on it. When you press the power button start tapping the ESC key and the UEFI/BIOS menu will open. Select diagnostics and test everything for errors. If the hard drive fails or it says you do not have a hard drive, then you're going to have to get a new one and order the recovery DVD from HP. If everything passes, it sounds like the OS is corrupted.
The next thing you want to try to do is run a Windows System repair disc to see if it can fix the problem. With any luck it might find a problem it can repair. If you do not have one and can find someone who has the same version of Windows you do then you can use the link below to make one.
Windows 7
http://windows.microsoft.com/en-US/windows7/Create-a-system-repair-disc
For Windows 8 and above systems.
http://www.howtogeek.com/131907/how-to-create-and-use-a-recovery-drive-or-system-repair-disc-in-windows-8/
If you have Windows 8.1 you can create a install/repair thumb drive with the link below. This will allow you to try to repair 8.1 first and if that does not work do a fresh install. Make sure you have a good product key and all the drivers before starting a fresh install.
http://windows.microsoft.com/en-us/windows-8/create-reset-refresh-media
If you downgraded to or have 10 you can create a install/repair thumb drive with the link below. This will allow you to try to repair 10 first and if that does not work do a fresh install. Make sure you have a good product key and all the drivers before starting a fresh install.
https://www.microsoft.com/en-us/software-download/windows10
After you make the thumb drive you can try restore it to the last known good configuration and that does not work you can reset it back to the beginning.
http://www.tenforums.com/tutorials/4588-system-restore-windows-10-a.html
http://www.tenforums.com/tutorials/4130-reset-windows-10-a.html
If that does not work then the next thing you want to try to do is recover your files. For this you will need a bootable thumb drive(flash drive) so you can boot the lappy. This will also allow you to verify that the lappy and its hard drive is good and all you have is a Windows problems. To boot the system you need to make a bootable thumb drive. You will need to find a working puter to download Unetbootin USB installer. You need to read the instruction carefully and know a little about Linux to use this. There can be dragons present if you do not understand what your doing. I make no guarantees.
http://unetbootin.sourceforge.net/
Once you make the bootable thumb drive you need to add a OS for it to boot. I recommend Linux Mint ISO. Its UI is similar to Windows. Download Cinnamon 32bit.
http://linuxmint.com/
If you have a Windows 8 or above then you need to turn off secure boot and select boot from USB before using the thumb drive. The thumb drive boot will also allow you to check out the rest of the puter. It helps to have a thumb drive or a external drive hooked up when you boot so you can copy your data and files to.
If it has a CD/DVD you can burn Linux Mint ISO right to a CD and boot with it.
Once you got the bootable thumb drive created, insert it into one of the USB ports. Also plug in the medium you selected to copy your files to. Press the power button and start tapping the ESC key. This should bring up the boot menu. Select the USB thumb drive and it will boot to a menu asking if you want to start Linux Mint. Click on Mint and let the system boot. Find your hard drive and copy your files to your back up medium. If the hard drive is a SATA drive it will show as sda. If it has partitions then the first partition (C Drive) will show as sda1, the next partition will show as sda2 and so on. If you have 2 drives the next drive will show as sdbx. X being the partitions if it has any. Normally external drives show as sdd or sde. I have seen Linux recover data that people claimed could not be recovered. Keep in mind while looking for your files, and this is a Vista or above version of Windows, that you have to find your USER folder. The folder will look something like this. \Users\nameofuser\Documents. Repeat that for music, pictures, and videos.
Once you have that done you can shut the lappy down. If you were able to save your files then you are half way home. Unplug the thumb drive and back up medium.
Since the repair options are not working your best bet is to reset the lappy back to factory settings as if it just came out of the box. Lets see if the hard drive can be made to boot again. This will erase everything on the hard drive.
If your resetting a lappy, make sure you have the AC adapter plugged up. You do not want this process interrupted. This should take one or two hours. It is best to check on it to make sure everything is going fine.
IF your lappy came with 8 installed, there is a good chance that fast boot is enabled. That will make it very hard to get to recovery until you turn it off. To turn off fast boot, press the power button and tapping the ESC key until you see the BIOS/UEFI screen. Click on the security tab then click Secure Boot Configuration. At the bottom you will see fast boot enabled, click fast boot and click disable.
Try recovery from the BIOS/UEFI. This is my preferred method.
When you press the power button start tapping the ESC key and the UEFI/BIOS menu will open, select the recovery mode. This will reset your puter back to factory settings.
This is what a UEFI/BIOS menu will looks like. Yours might be different, I am posting this one to give you an idea of what to look for.
F1 = System Info
F2 = System Diagnostic
F9 = Boot Device options
F10 = UEFI/BIOS Setup
F11 = System recovery