Hi,
My best guess at this point would be that the problem is hardware related.
You could try a 'Factory Reset' ( in fact, HP may well ask you to do this anyway before sending the machine in for repair under warranty ). The procedure can be found in the document on the link below.
Performing A Factory Reset - Windows 8.
If this doesn't correct the issue, this would pretty much confirm a hardware issue and it'll need to be repaired.
If you live in the US, contact HP Here.
If you are in another part of the world, start Here.
Regards,
DP-K