Precision 3630, POST stuck at DELL logo

I have an i9 Precision 3630 with a RX590. Last week I got a 32 inch LG Ultragear monitor. The system boots into Win11 as long as the monitor is not connected. Have tried both HDMI ports and the Graphics port. Still hangs at POST. Also tried two hdmi cables. After connecting the monitor after POST, all is "OK". Work around is to have monitor connected while I am using it. Disconnect when not, so that updates etc can be done. Does anyone have any suggestions. Thanks in advance.