Not familiar with OpenElec, sorry. what version of Linux?
Are you tryng to instal LInux on that HP pc? or just try the Linux out in RAM memory?
Have you tried installing the Linux to your built-in hard drive? if not, you should attempt that. does the HP still run Windows? if not running Windows you may have a faulty hard drive or Motherboard; either of these when faulty can prevent an OS from booting thru the usb port.
What is the purpose of you running this "OpenElec"? if you would provide us with answers to all these questions we can better advise you.
Lastly, have you tried disconnecting your hard drive and running the usb flash drive? if that works, it indicates your hard drive may have failed and needs to be replaced. you can download free Seatools drive diagnostic from link in my Signature below and run BOTH short and long tests on drive. if you get any errors back your drive has definitely failed and you will need to replace it.
BIGBEARJEDI