How to boot a P771ZM with an old SDD as the only or primary drive?

My P771ZM just arrived this morning and fortunately I was able to connect and access my old SSD without problems. However, I'd like for a moment to have the old SSD to boot as the only or primary drive, since I need to check things like programs installed and other settings that are not visible when the drive is connected as a slave.

So since I don't want to break anything, is there a way I can disable the new and current primary m.2 SSD without having to physically disconnect it, so that the old one will boot instead, and then re-enable it when I'm done? I think maybe within the BIOS I should be able to do this?

Another thing. The old SSD has a Windows 7 installed while the new one a Windows 8.1. Does booting the laptop in a different OS affect the BIOS or anything else in any way?

 

several things to consider:

- your M.2 SSD is configured as a GPT partition with an UEFI install, whereas ur win7 is most probably MBR partition with a BIOS / non-UEFI install. thus, u have to go into the bios and disable UEFI boot under boot options. remember to enable that setting again before trying to boot from your m.2 ssd! otherwise it wont...
- once done, u can press F7 to get into boot options during boot and select the old ssd that u would like to boot from. i would recommend installing that ssd into the machine first before doing that. it might work from external usb but not as likely as an internal drive
- do not be surprised that the win7 could be messed up due to non-matching drivers / utilities / windows being deactivated due to motherboard change. but if this is just to check some data and make a quick backup, it should suffice. DO NOT use it as a daily driver though!

 

Thank you, it worked without problems! +2 reputation

 

For some reason though, now about half of the times when I boot or reboot the computer, instead than loading straight into Windows, it goes to a black screen where a white text says

"Reboot and Select proper Boot device
or Insert Boot Media in selected Boot device and press a key".

Pressing any key simply makes another identical message be displayed below the first one, so I can only hold the power button to reboot again and then it goes into Windows normally.

I'm pretty sure I reverted the changes I touched into the BIOS correctly, so I'm not sure why I'm getting this some times (about half of the times only).

What could be causing this behaviour?

 

are u sure u have re-enabled uefi boot? try and disable fast-boot while ure at it, see if that fixes the issue...

 

Yes, UEFI boot is definitely enabled. I didn't find any fast-boot options. Here's what I see:

 

looking good from that end. try and re-seat the M.2 drive, make sure the contacts are clean and the drive installed properly / firmly without wiggle.