Blank screen on boot

Got a laptop to fix. For some reason after a shutdown the hard-drive corrupted. I assumed it was a hard drive problem, so tried with another hard-drive and that seemed to work.

Everything was going fine, I install Avast, reboot and get a bluescreen with "Stop : 0x000000a5 ..."

After a quick google it showed me that it could've been a bad memory seating, so I took the memory out and replaced it.

Rebooted again and all I got was a blank screen. Tried the powercycle thing (Hold powerbutton for 1min+ without any power/battery connected), switched memory out with a (known) working memory. Still nothing. Any thoughts?

Also tried connecting to an external monitor (tv screen) but don't know if it would show if it's still in BIOS/Bluescreen(the 0x000000a5 thingie) so not sure if it's screenrelated. Any ideas on how to check that for sure?

Laptop is an Asus X55a.

EDIT: No beeping sounds either, the harddrive is however spinning.