Startup issue with my HP Z820 Workstation server

Hello, I had to work on an HP Z820 workstation server last Saturday. I had to remove a 4GB RAM module to insert it into a desktop computer, which didn't work, and when I put the RAM back into the server, it no longer operates normally. As soon as I plug it in, it lights up for 3 seconds and then shuts down. I don't understand why. Please really help me solve this problem because this server hosts an application for a company.
And I would also like to know if desktop RAM is identical or compatible with server RAM. Thanks in advance.