Resolved Second monitor with mid-2011 iMac: failure

[rosegeorge]

hello all. I've got a mid-2011 iMac running High Sierra 10.13.6. A few years ago, I successfully used a second monitor with it (an Acer). I've just bought a Dell monitor to use with it, but although I've tried two VGA cables with a thunderbolt adapter (one cable is brand new) I cannot get them to connect. The Dell says there is no signal; the iMac doesn't detect the Dell.
Dell specs:

DELL U2412Mb 24" Widescreen Ultra Sharp LED-backlit Monitor VGA DVI-D DP USB HD​

I haven't yet tried with DVI-D but that may be my next thing. I've tried to connect the Dell to the Acer (that used to work fine): still no signal.

Any suggestions? Is there a way of finding out if the thunderbolt port is faulty? is the iMac just too old to cope with the new monitor? It runs fine otherwise, on 16GB RAM.

All advice appreciated.

 

[rosegeorge]

Update: I can't see how to delete the post or mark it as resolved. But it is resolved: the issue was the thunderbolt adapter.

 

[TheShortTimer]

Update: I can't see how to delete the post or mark it as resolved.

Click on the three small circles beside "WikiTools" at the top of your first post and select "Edit thread" and in "Title" you'll see the option to select "Resolved."

 

[Amethyst1]

Update: I can't see how to delete the post or mark it as resolved. But it is resolved: the issue was the thunderbolt adapter.

The easiest way to connect the monitor would be a DisplayPort cable. The iMac’s Thunderbolt port is also a DisplayPort output.