Hello,
Thank you for posting in the HP Support Community,
Your model usually comes with Windows 7 preinstalled and should have a COA sticker with Windows license key on it. The COA sticker may be on the bottom of the PC or behind/below the battery. You need to check this on your own.
The sticker should look like this:
If the legitimate/original Windows 7 version is now installed on the PC and you can boot it (start it) successfully, you may use a program from NirSoft known as ProduKey to see the key.
Download ProduKey from Nirsoft>> http://www.nirsoft.net/utils/product_cd_key_viewer.html
x86 Windows >> http://www.nirsoft.net/utils/produkey.zip
x64 Windows >> http://www.nirsoft.net/utils/produkey-x64.zip
Extract the archive and run the program.
It will open and show you the available keys it detects. Does it detect your BIOS and Windows key(s) ? Does it says Windows version ? Take a picture of the Windows code and write it down. Do not post it here, just keep it for yourself.