RAM upgraded and iMac mid2011 beeps

The memory integrity check failed, but the reason may not be limited to bad RAM. It could be an intermittent electrical socket connection or related logic board flaw. Try removing and reinserting the original memory modules and swapping their locations. Make sure they are firmly seated.

If your Mac beeps during startup - Apple Support

Mac's are very picky, what RAM modules did you use?

If firmly reseating the new modules dose not work, reinstall the original modules, return the new modules and purchace modules directly from either OWC or Crucial.

https://eshop.macsales.com/shop/memory/iMac/2011/DDR3_21.5_27

https://www.crucial.com/compatible-upgrade-for/apple/imac-(21*5-and-27-inch--mid-2011)-imac12-1-12-2

Tip: lay the iMac facedown on a soft cloth and firmly seat the modules with your thumbs.

see > Install memory in an iMac - Apple Support

not sure if this will help, but make sure the RAM is installed correctly, then try to reset the SMC:

https://www.makeuseof.com/tag/reset-macs-smc-pram/

Maybe try to use one single RAM stick at a time to see if a particular RAM stick is causing the boot problem. Kind of rare, but maybe one of them is bad?

Like some others I suspect modules that are not fully seated, especially if the computer was fine before.

Our 2011 iMac requires a heavy push to fully seat modules. We have to hold or otherwise support the far side of the case to get enough force.