GIMP 2.8.? and MATE 15.10
I now have Synaptic and will try this.
From terminal, I got several errors–GEGL???
Open Synaptic and search for "gimp", then right click it and mark for re-installation and then on "Apply":
Synaptic exhibits the same problem I have with GIMP. Initially, it asks for a password. Then, as with GIMP there is no window for interaction with the software.
How did you install your version of Ubuntu Mate, Live CD or USB drive?, see the following link please because I suspect you have a faulty install?:
I used live DVD.
Sorry if this has been asked before, but if I try reburning and reinstalling, how do I not lose things I have already installed that do work?
You can use this thread to re-install with a live CD burned at the slowest possible speed!:
You will still have to re-install any extra apps you require though but it will maintain your settings and any files you created!. 
I used a newer Mac to burn the DVD. The Mac burner does not offer but one speed. I may just wait for the next generation of Mate. Most things are working. I did create a bootable USB but I think my G5 Mac is too old to boot from it.
Hi,
I don’t have a MAC but I would assume that somewhere in the burner app settings, there is (should be) a burn speed control function somewhere?.
There is an option available but the DVD had a slow enough burn rate to force the slow burn.
Too many things work right for me to try the radical step of reinstalling right now. GIMP was mostly a wished-for option.
Hi,
try running the following terminal commands which may/may not solve the hardware problem for you?:
sudo apt-get --fix-missing install
The above command downloads and installs any missing packages on your system.
sudo apt-get --fix-broken install
The above command downloads and installs any broken dependencies on your system.
@wolfman For Ubuntu MATE 16.04, please start directing people Welcome. You’ll find one-click solutions for those type of issues 
I ran this and no changes we made. But, thanks for the suggestion.
Sorry Wimpy, I keep forgetting that!. 
He is running 15.10 though!.
Just helping get you prepared for 16.04 ️
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Just to get slightly off topic Wimpy (a lot actually!), I’m almost finished with the German translation, only 2 and a half more folders to go!.
@tomi, can you not burn a new disk using a friends computer?.
You said earlier GIMP produces GEGL errors from the terminal, – indicating the GEGL library is part (or just) the problem. Have you got any full terminal output for us to investigate?
GIMP should work on PowerPCs, it could be the case of corrupt packages or some strange problem running on the Mac G5.
I took a screenshot after running gimp in terminal. I will try to insert it. There were many lines like those involving GEGL-gegl-operation.c that I can send if necessary.
I discovered that GIMP is (has always been?) running. By accident, I tried opening a jpeg file with Ctrl-O. A window appeared that allowed me to choose a file. By choosing KEEP the embedded profile, I could see and edit the picture. I could save/export it as normal.
Now, if I can figure out how to get Synaptic to work.
I tried to download Darktable through the Ubuntu Software Center but was told it was not available (even though it showed in the Software Center and even allowed me to click on Install.