I get random crashes when i m playing heroes 3. I tried compatibility mode and administrator, I use windows 7 and my processor and graphic are ati .
Any ideas ?

Do you have a multi-core processor? If so, then that could cause some issues on several GOG games. There are posts on this forum about HoMM3 crashes that recommends using the program imagecfg.exe which you can find here: http://www.robpol86.com/index.php/ImageCFG

See the instructions:

Thank you potato_head it worked perfectly i'll know what to do next time.

Bumping and also requesting this be stickied.

Sorry for gravedig, but for this fix, I just put this cfg exe in my system32 folder, and then add that imagecfg -a 0x1 to the start of my HoMM3 shortcut, correct?

No.
You use IMAGECFG to permanantly patch the HEROES3.EXE file (or the Heroes3HD.exe file if you've already applied the high-def patch). Once you've patched the EXE then you use that. You no longer need IMAGECFG.EXE afterwards.

Of course, make a spare copy of HEROES3.EXE in case you mess it up the first time.

Just to let you know.

If you don't want to modify your game exe or use any third-party software, you can use the following fix:
1. Create a game shortcut with the following path:
[code]C:\Windows\System32\cmd.exe /C START "Heroes3" /affinity 1 "[game path]\Heroes3.exe"[/code]
Still I'm not 100% sure if this will work as I could not set it up yesterday :D I remember it was working previously so there might be some errors in the syntax.

2. Create a text file with bat extension (Rightclick -> New file -> txt and select a name -"Run Heroes3.bat" in my case. You might have to disable "hide known extensions" if running Windows XP), edit it and inside of it enter the copy the following:

Oh, alrighty, thanks for the clarification.

I hate to bump this topic, but how do you make the IMAGECFG work, I'm not experienced with using things like that, and can't seem to figure out how to apply it to HoMM3/chronicles.

Detailed instructions on how to use the ImageCFG program can be found here.
If you don't understand this instruction I recommend you to play this game on a legacy computer with single core processor and Windows XP (32-bit x86) operating system.

I've been using Heroes3HD and haven't had any issues. It also allows for higher resolutions which is really nice on larger screens. I have a quad-core Win-7 64-bit machine with an ATI 6950 and also a Lenovo T410 and both run fine with Heroes3HD.

Heroes3HD information and download.

I had no issues for a month or so after I started playing Homm3 with my quad-core. Then I stopped running Seti@home. Then other cores weren't 100% busy all the time and I had the crashes frequently until I patched the program with imagecfg.

I also didn't have any issues with Heroes 3 for the first month or so. It only started to crash when I began playing really large campaign maps, so I assume that all of the single scenarios and smaller campaign maps were only actually using one core. But on the bigger maps I'd be crashing every 5 minutes or so. ImageCFG worked absolute wonders for me.

The actual specific way to force Heroes 3 to use only one core using ImageCFG is posted here, courtesy of Tarnum.

I found this on another forum. I applied this fix and it works! no more crashing!! This post was done by rampart3, I do not take credit for this fix:

On Win7, I had crashes to desktop about once an hour. Changing it to XP SP3 compatibility mode caused it to lock up in the repeating sound loop about once an hour. What did work was to run on one core with NO compatibility mode set.

To make this easy to do once set up, in the same directory as Heroes3.exe, I created a new text file called 'Heroes3.bat'. Into this 'Heroes3.bat' file, paste the following three-line script:

@echo off
start /wait /affinity 1 Heroes3.exe
exit

Now start HOMM3 with a shortcut to this 'Heroes3.bat' file. The advantage of this is that once set up, you can just play without thinking further about it.

I have 20 hours of no-problem play since doing this, half on a Vista laptop, and half on a Windows 7 desktop.

(Another tip that works: I keep all HOMM3 files on a USB stick so I can continue a game on any computer without bothering to install it again.)

I tried this with my dvd version and played for about an hour without problems before I quit. If this solution works in the long run, then I would recommend this rather than using third-party software. It is very simple and there is no risk of any malware since you don't have to trust someone elses program.