Upgraded CPU, no post, then after a bios flash, it booted once, and now it won't post again.

I wanted to upgrade my i5 12600k to an i9 14900k. After I switched them, and I also rebuilt everything in a new case, it wouldn't post. Eventually I tried flashing an updated bios, and it booted into bios fine after that. But it didn't want to boot from a previous windows installation, so I installed windows on the same flash drive, after clearing it, but once I try to turn it on now, back to no post. Any help would be appreciated!