Sory for my Engl.
I has same problem in dv6-3125er - black screen after change bios options.
I try do something 3 days, and want go to service center...but repire himself:
First of all - remove bios battery, then withou battery and charger push Power button 15 seconds.
Put back Bios battery, battery..
Prepare HP_tools flash with 55299 bios from HP site (unpack 55299.exe, use phoenix tools to unpack 01448F29.bin, then rename one to 01448.bin, rename RSA.sig to 01448.sig - put it together to flas in folder "current" only)
Put flash HP_tools, hold Win+B
Put recherche cable
Push Power (Win+B - hold untill LED near recherge cable change color from orange to white) - near 15 seconds...
After start recovery
P.S. if you change memory sticks - put it back stricktly in place, where they stay befor you install new BIOS !!!