Updated the BIOS - not easy when you don't even know what a BIOS is, but completed successfully.
Doesn't make any difference though.
Next is the chipset drivers, will be on the same page that you got the bios updates
Have a read here as well
http://support.hp.com/gb-en/document/c03383935
When i worked for B&Q, we put in 6000 HP machines, these were a mixture of laptops and desktops, most were fine but about 30% had this wake up issue, its a pain some where fixed by the bios update, others the chipset.. some we ended up turning off sleep mode as nothing would resolve