Well it sounds like you were running a BIOS MBR set up that needs CSM to boot. That setting didn't change its self because you opened the case to clean it. Just go back into the BIOS and change it back to enable CSM.
If you are having Black screen with computer running would check the cable and connections for the monitor.
Its possible to flash back your BIOS using Winflash but you have to get into windows to use it. However disable is he default for CSM
Since you had just dissemble your notebook I would look for cables that are damaged or not correctly connected logically that where the issue should be
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro