XPS 17 9700, U2721DE, no USB-C signal

Hi.
I have xps 17-9700 laptop (2021) connected to the dell U2721de monitor via usb-c to c cable. Nearly 3 years pasting i have sometimes problem issues about connection that "no USB type C signal from your device" but when i disconnect the cable and then connect again it works all time.
But 3 days ago i get suddenly the same problem that "no USB type C signal from your device" but cannot solve with any solutions in the community forum. i plug-in all cables, disconnect and connect power cable, restart and update laptop, update and uninstall-install dell display manager etc.etc. but there is no respond.
But when i connect usb-c cable, it gives power, external keybord working etc. but no signal to the monitor.

Is there any other solution about this? 

Please help me...Thanks...