[SOLVED] PC Keeps Booting to BIOS

[WhatsAComputerMachine]

I recently changed my CPU from an Intel i7-7800X to a Ryzen 9 5900X. Of course, the motherboard was changed as well but nothing else changed.
Now, every time I try to boot my PC it goes into BIOS. The motherboard is MSI B550 Tomahawk with latest version of BIOSed (I flashed it an hour ago)

First, I tried reinstalling Windows, and it told me to boot the PC using the existing operating system before updating. However, when I tried to do that it simply kept going into BIOS again and again. Since then I have cleared CMOS, flashed the BIOS, and disconnected every drive but my main one, and all peripherals excluding mouse and keyboard (other cables plugged in are HDMI and Ethernet). When I look in BIOS, it is able to detect the drive that I am trying to boot. I really don't know where to go from here so if anyone has any suggestions they would be very much appreciated.

Ryzen 9 5900X
MSI Tomahawk B550 MB
32GB (4x8GB) Corsair RAM
GTX 1080 Ti
750W PSU
2TB Samsung SSD

 

[RNGITproblems]

What's the make of the old motherboard?
Maybe you need to enable legacy support or some other boot options.

You can see the OS drive in bios but it doesn't boot? If you try to boot that drive does it kick back to bios or go into win recovery?

 

[rocktalkrock]

When you are in the BIOS have you looked at the Boot device priority?

 

[scout_03]

the new install did not work you still on old system with os so you need to boot from a usb with the os and when it ask boot to erase old partition say yes .

 

[rickypicky5]

How did you create the drive you are trying to boot from?

Create installation media for Windows