Well, I bet you are at least relieved to have isolated the problem.
Sounds like you will be working with AMD support. If your are interested, see if they will add you as a driver beta tester. I think you will be good at it.
Do you open SU on your primary monitor?
BTW, there’s other paths to get to the place to rollback drivers in Windows. Start > r-click on Computer > Properties > This open a page in your Control Panel. Choose the Device Manager > Display Adapter > r-click on the graphics card in question > Properties (this get you to the roll back button.
You also can go through Start > Control Panel.
Sorry for the delay. I wanted to go full circle on this for the benefit of others in the future. I re-updated my AMD/ATI Radeon 5450 driver to whatever the latest version the online automatic search updated it to. My brand new Acer 27" HD monitor is making use of all its spectacular glory. I re-verified all the previous headaches as stated in earlier posts. I then re-rolled back my AMD/ATI Radeon 5450 driver. Acer 27" HD back to looking like 24". ;'(
Verified again that SU is now working correctly with “Use hardware acceleration” checked.
BUT HERE’S THE KICKER!!!
SU 2016 (16.0.19912 64bit) is now working too!
So it does lean towards an AMD issue and, Yes! I am happy/thankful for the isolation because now I can get back at my file that was saved in SU 2016 and do not have to redo all that work. Worth forfeiting a little screen resolution issue on a brand new monitor temporarily until they get the kinks worked out.
Sorry, but I must reiterate:
LESSON LEARNED, MAKE BACKUPS OF YOUR PROJECT FILES IN THE VERSION OF SKETCHUP YOU ARE UPGRADING FROM.
The same OpenGL function - provided by the AMD graphic driver - SU uses to save files applies to SU14-16.
I’m glad you are back in business 
…and yes, SketchUp starts on my primary monitor. However, if I happen to close the SketchUp window in another monitor and I restart SU the splash screen starts in my primary monitor but after clicking the “Start using SketchUp” button the SU window starts in the same monitor location it last exited (and there is a corresponding SU window icon in the task bar too regardless of which monitor the SU window is in).
I wanted to add one more thing. I kept playing around with SU 2016. As long as START SU 2016 with “Use hardware acceleration” un-checked, I can update my AMD/ATI Radeon 5450 driver to whatever the latest version the online automatic search updates it to and use the new Acer 27" HD monitor in all its spectacular glory. It’s only when I set “Use hardware acceleration” to checked then, exit SU 2016 and attempt to restart it is when I get back to the original reason I created this topic. Does anyone know of a command line switch to start SketchUp with “Use hardware acceleration” un-checked? Something like “C:\Program Files\SketchUp\SketchUp 2016\SketchUp.exe -X”. Like a “safe” mode?
Sure would be nice to have that option since interfacing with OpenGL is sometimes problematic.
One thing that could be causing your problems is the USB adapter, I run four screens but I did have some problems getting them to behave at one point after an MS update.
I eventually found that I needed to uninstall the USB Hub and most importantly the Drivers. There were two entries that could be uninstalled using the add remove function, Display Link Core Software and Display Link Graphics.
I removed them, got the other screens working properly then reinstall the software and driver for the USB Hub and all worked again.
Just a thought, who knows.
Work with AMD to get a better driver ;). Most die-hard SUppers use NVIDIA cards which contain more complete OpenGL support. OpenGL is the name of a specific suite of function calls. Most people associate it with depicting 3D graphics seen on the 2D monitor screen. Leave out some function calls, SU tools many not work, SU many not even open for others. And and this thread demonstrated, saving files and exporting also can be affected. When SU recommended hardware/software states 100% OpenGL compliance, it’s not joking. SU uses some OpenGL functions that other applications don’t use. And sometimes driver developers that cater more to those other applications leave things out.
Something in that old, functional driver is missing from the new driver. You are a loyal AMD supporter and shouldn’t need some jerry-rigged hack to enjoy your hardware.
And Box is right, check for other naughty drivers.