Question : My ESXi server guest OS's keep powering down unexpecdetly

I have an ESXi sever that I built on hardware I bought from various places. The server has been working with no issues for months. All of a sudden, the guest OS's (all windows) keep powering down for no reason. When this happens my vSphere client forces me to reconnect. I am brand new to ESXi and I don't even know how to start troubleshooting this.

I checked for disk space in the data store and I have over 200GB free in each datastore.

Answer : My ESXi server guest OS's keep powering down unexpecdetly

When you say vSphere client forces you to reconnect, it seems to imply that your ESX host is rebooting. If the guest powers down, but the ESXi host continues to run, you should not be forced to reconnect to your ESXi host.

Can you confirm if your ESXi host is rebooting?