Been playing M&M 4-5 for a couple of days. Today when I clicked my desktop shortcut, the DOSBox opened then my computer rebooted itself.
I tried againand the same thing.
I tried again, the same thing.

What's going on?

OS: Windows 10
CPU: Intel i7-6700k 4 Ghz
GPU: GeForce GTX 970
RAM: 16GB
SSD: 120GB
HDD: 2 TB

Sat 12/10/16

Latest observation...
Sometimes when I start the game the DOSBOX window opens, the orange DOSBOX logo appears and the game runs fine.

Other time when I start the game the DOSBOX window opens, NO orange DOSBOX logo appears and the computer reboots.

Extremely frustrating. Ready to give up.

12/24/16
OK everyone, problem solved.
Problem was with the nVidia 3D setting DSR. It has a conflict with DOSBOX. I turned it off and everything runs great.
Confession: this solution is actually described by GOG in the help section. Sadly, I failed to see it when I first searched for a solution. My bad! Cudos for GOG!

And my thanks to the many people who took time to reply on this forum. Great community.

Now, back to the game.

Could be virus/malware.

Or it could be some "benign" malware, like Microsoft in their infinite wisdom rebooting your machine instead of giving you the Blue Screen of Death with accompanying error message.

But first I would check that shortcut, see what it points to and the check out the file it point to.

Could also be drivers or hardware. Double check Win 10 didn't change your GPU drivers in particular.

The Shortcut is as supplied by GOG.
"D:\Games\GOGLibrary\Might and Magic 4-5\DOSBOX\DOSBox.exe" -conf "..\dosboxMM4-5.conf" -conf "..\dosboxMM4-5_single.conf" -noconsole -c exit GeForce Experience says I have the latest nVidia drivers.

As I implied earlier it could be a cause of Windows rebooting instead of showing the BSOD screen, which is default in at least some Windows versions. It was driving me crazy some years ago when my machine would reboot every time I started a certain program. I thought I had some virus, but it turned out not to be. I don't remember the details, just that I was astounded and disgusted to learn that the defaul behaviour of Windows is to reboot instead of showing BSOD with error message.

Could be the same thing happening here, so it might be worth trying to find out how Windows 10 handles such situations, if it just reboots instead of BSOD. If it is the case than an error message at least would give you something to work on. Unfortunately I have forgotten all the details.

Try running DOSBox without MM4.
Try changing the graphics options.

See what happens in both cases.

Another forum, a short time ago:
"Using the wrong kind of sound option makes the game crash as it tries to play the sounds/music, choose another sound option."

Could be relevant.

That is very odd. Not sure why it would work sometimes and not others. If you haven't tried it yet, fully uninstall and then reinstall the game (and maybe even uninstall and reinstall DOSBox) and see if that helps. Also, check which DOSBox version comes with the games... I recall that when I played MM1 it was using an older version (I think 0.72) instead of the latest 0.74. I'm not sure if that's changed, or if it's different for MM4+5.

Also, for MM4+5 there are two versions available, the original floppy disk version and the CD-ROM version with extra digital speech. Try running both and see if one works better than the other. If the floppy one works better, then the CD version might be having issues with sound settings (since it has extra sounds).

Do you use DOSBox for anything else? Does it work for other programs?

I've uninstalled and re-installed twice. no change in behavior.
I use the DOSBOX program provided by GOG. I don't use it for anything else.
I'm sad I can't play those games. Bought them from GOG hoping to relive some hours from the 1990s.
Well, time to move on to something less frustrating. Lots of great games out there!

Try the following.
Open dosboxMM4-5.conf in the folder where you installed the game.
Search for the line:

cycles=max

Change it to something like:

cycles = 10000

See how it goes.

Assuming a properly written OS (and Windows 10 ought to qualify for that label), DOSBox can't cause a spontaneous reboot no matter how badly it behaves. I wish you luck in whatever game you pick next, but unless you solve this, I suggest not buying any other DOSBox based games. You might find that they also cause a spontaneous reboot.

Before you give up, make sure you try running both the original floppy version and the CD "talkie" version. The GOG release will install both of them. It's possible that one will work and the other won't, I've seen some players reporting that.

Try opening dosbox without running mm4. Then try running mm4 manually from it. This will at least help figure out if it's dobox or mm4 thats causing the reboot and perhaps help ussolve it.