Windows 10 corrupted: Need to get into safe mode

Windows booted up fine after the replacement and started updating I walked away and came back to a blank screen (As in the monitor was in stanby mode but the computer was on) and could not get the monitor to come back on. I restarted the computer and it booted normally getting to the windows logo and finishing and then the monitor goes blank into standby mode. If I wait an hour nothing happens still. I have tried using startup repair from the installation disc it says it failed. When I force the advanced options to come up (interrupting boot 3 times) I can't use my mouse or keyboard to click on anything. Now I'm struggling to get into safe mode to run DISM to repair the installation however I'm not sure how to. I've tried the F8 method which of course does not work. I've tired using the installation media and repair my computer and there is no option for booting into safemode. I'm not sure what next step I should take...ideas?

Note: My PSU went bad and I just replaced it.

Thank you essenbe but since I can't get the OS up that leaves three options for me. A recovery drive which I don't have, Hard rebooting during startup which does bring up advanced recovery but my mouse and keyboard won't work and I've tried other mice and keyboards, and finally the installation media where the startup options are missing altogether for some reason (Going under repair computer and then troubleshooting as well to look for startup options).

Sure no problem. Ok so I noticed it failed at the point when my bios indicated there was an electrical output problem upon this I tested it with a multi-meter and the voltage is inconsistent. So I swapped it out with a better model (1200axi). I booted it up last night and windows loaded without issues and began the process of updating windows through windows update and I believe the GPU and Norton were updating as well. I walked away and came back to a screen in standby mode and the computer on and was unable to wake it. Upon restarting it loads up past the windows logo and I get the same weird standby mode.

Bios has video and so do live cds. As I said I can't get into windows so I can't quite get to safe mode. Advanced recovery options do not respond to any inputs. The installation media does not bring an option for safe mode either under repair.

In other words reinstall windows. Understood :) ( I am using a usb hardwired mouse and keyboard)

Just confirms what I already figured was the only option.