Desktop PC troubleshooting on 2 computers, one not booting to Windows, no video output on the other

I've got 2 desktop computers to look at today. One isn't booting into Windows and is instead going to the main bios screen. The 2nd desktop was recently upgraded to a 10th gen CPU and a new motherboard. Since then the client hasn't been able to get video on the monitor.

Tools used in this video
https://www.techpowerup.com/download/...

https://www.hwinfo.com/download/

You can purchase the tools I use in my videos using the Amazon links below.

Arctic Silver 5 AS5-3.5G Thermal Paste
https://amzn.to/3E1AGSW

DataVac blower
https://amzn.to/3ozYSpL

This is the powered screwdriver I use in the video. Metabo HPT Cordless Screwdriver Kit
https://amzn.to/3xNzgqz

This one I keep in my car for mobile work. It's very good and much cheaper that the iFixit kit
https://amzn.to/3LasanN

This is the one I have. It has the same 64bit set along with some other useful tools and a carrying case.
https://amzn.to/2Shdjfr