The Heroes Round Table

Backstory of Heroes 1-3 is connected while HOMM4 and 5 have separated world and story. For old games check *** many old games which are legaly downloadable can be found there. *Link removed, although it's right what you said, here's also dark side of it. Furthermore this legality is strictly dependi...

I had similar problem with Disciples II: Dark Prophecy .
Game was trying to make monitor refresh frequency over 100Hz while normal was 60-70 and monitor would turn off to prevent damage.
Sadly i'm not sure where to find screen refresh rate meter for HOMM5 but i think this is your problem.