External monitor detected but receiving no signal (Ubuntu 24.04)

I have a Lenovo Thinkpad T440P connected to an ASUS VG278Q monitor. The thinkpad is running 24.04. The monitor is detected (xrandr gives the following:)

xrandr --listmonitorsMonitors: 2 0: +VGA-1 1024/271x768/203+1600+0  VGA-1 1: +eDP-1 1600/310x900/170+0+0  eDP-1

but the thing still shows 'no signal' and stays in sleep mode no matter what I do. I am using a cable connecting the VGA port on the Thinkpad to the Displayport port on the monitor. I have tried all of the recommendations I have seen available online to fix the problem in Ubuntu 22.04 (where I originally had this issue), and eventually upgraded to 24.04 in the hopes it had been fixed. No such luck.

If you have any insights I'd love to hear them. Thank you very much.