iMac will not boot up after installing two 16 GB RAM

Macs are incredibly picky about RAM.

Remove the memory you installed and replace it with the original Memory if necessary.

This is pretty much the only source most senior members here recommend for RAM: https://eshop.macsales.com/

Most of the RAM you can buy at your local computer shop or online isn't really spec'd properly for Macs.

How To: Install memory in an iMac - Apple Support

Note: Late 2014, Late 2015, Mid 2017, and Early 2019 all use different types of RAM. It is important to correctly identify your Mac and purchase the correct RAM! Which iMac do you have and what kind of RAM did you try to install?

Crucial is another reliable brand known to work with Macs.

+1 on Kilted Tim's, he is 150% correct. Please uninstall the RAM you installed and buy the correct RAM from www.macsales.com!!!!!!!!!!!

HWTech wrote:

FYI, I don't think Crucial is selling Mac Compatible memory anymore specifically for Macs.

Crucial has flagged their Mac compatible memory as end life, but there is still remaining stock available at 3rd party resellers (while supplies last). Mostly I was trying to point out that working memory isn't exclusive to OWC. OWC just happens to combine good quality with a really good website for matching buyers to the correct memory for their model and avoiding confusion.

padams35 wrote:

Crucial is another reliable brand known to work with Macs.

FYI, I don't think Crucial is selling Mac Compatible memory anymore specifically for Macs.