Why would a CRT monitor stop displaying higher resolutions for one computer?

"I truly doubt this is the case (and most often, this requires some human intervention), but: any chance your new computer somehow (and erroneously) updated the EDID in the monitor? Or: any chance the Display Data Channel (required for EDID) is broken in the cable or connector? (You're not using a KVM switch, right?)

Some monitors come with wrong factory EDID information, which then basically prevents one from selecting some resolutions or frequencies in the OS's display settings. For most systems these are just annoyances, and fixing the EDID then merely makes workarounds like ""show incompatible video modes"" no longer necessary.

In your case, you can in fact still select the very same resolutions that used to work just fine. But maybe the OS now thinks that this resolution allows for a higher frequency, or for non-interlaced operation while the monitor in fact does not support that?

Maybe software like Monitor Asset Manager 2.3 can provide some information? That will show you both the information provided by EDID, and the information that Windows has stored in its registry. If those are different, then maybe you can do a ""detect monitor"" or ""detect screen"" on your old computer? (For the sake of troubleshooting, I would first copy the information from that software before running any monitor detection again.)"