Your video card/video-drivers have to be new enough and have enough dedicated memory available before 3D will be activated.
Also check PS / Preferences / 3D and see how much VRAM is available. On my work computer I only have 221MB and this is not enough for 3D. The card, itself, has 256MB of video memory but some of that isnt’ available because other things are using some display memory. My home computer has 1GB of video memory with 1010MB available which is more than enough for 3D to work.
How many MB do I need? My Preferences says I have 988.
You should be able to do everything with 512MB so 998MB of VRAM if that’s what you mean, should be enough. Do you have Advance Graphics turned on in Preferences / Performance?
Do you have a separate video card or is it on the motherboard and perhaps shares memory with the system, and perhaps doesn't work due to that?
What OpenGL version is listed in Help / System Info...?
Do you have an RGB-color-mode image open?
When my computer doesn't have enough memory or I don't have an image open if it does, the only 3D options that aren't grayed out are Get More Content and 3D Print Utilities. Is that how yours looks?
Yes, everything is gray except those options.
The System Info says
OpenGL Drawing: Enabled.
OpenGL Allow Old GPUs: Not Detected.
OpenGL Drawing Mode: Advanced
OpenGL Allow Normal Mode: True.
OpenGL Allow Advanced Mode: True
I changed to RGB and now I can select it.
Thank you for your help.
What color mode was the document you were using when it didn’t work?
By design, the 3D menu's are only active for Grayscale and RGB color mode documents.