Question Windows 10 wont Boot after adding a second device

[whiteunicorn_uwu]

I hope someone can help me with my problem. I only have a 250GB SSD 2,5" in my pc. Now i wanted to add another one but since I added the second one Windows wont boot at all. There is only the blue Windows Logo with the dotted circle underneath and nothing else is happening. I can see both SSDs (2,5" both from Samsung (the one working is the 830 Series (with Windows installed) and the new one is a 860 EVO, both 250GB) in the BIOS. If I remove the new SSD my pc will boot normally. The MB is msi B450M PRO-VHD PLUS

Thanks for your help!

 

[RealBeast]

It sounds like your system is attempting to boot off the new drive. In the bios drive startup order with both drives attached, have you selected the old drive to be at the top of the boot order? Do you have your bios set to show the startup details instead of just a splash screen?