About this Mac not displaying

iMac

OS X El Capitan 10.11.6

Choosing About this Mac from the Apple menu does not produce the usual splash screen (or anything else)

Choosing System Information (same menu and position, with option key down) also fails to present the usual report (or anything else).

Both menu choices present the expected displays on my MBPro running the same OS version.

Suggestions?

Regards,

Barry