When I first downloaded (when it was free) it was working fine but then while I was playing it (a few days later) my computer crashed (nothing to do with the game my computer ran out of battery half way though a game)
Now whenever I try to play it there is huge lag when I try to do anything
I tried uninstalling and then re installing it but it's still just as lagy
Any ideas about how to fix this
I'm on windows 7

First try other games in-case the problem is with your laptop overheating. It could be throttling the speed of your CPU or graphics card to cope with high temperatures. If the same problem occurs, grab a can of compressed air and clean out the dust from your intake and exhaust fan.
I'd also make sure that you have up to date graphics drivers.

Make sure you are testing the game with the laptop power plugged in, as some laptops perform very slowly with games when using the battery.

Next, try loading the "Graphic Mode Setup" shortcut from your Start Menu > Dungeon Keeper Gold [GOG.com] and change the Graphic mode from "Surface" to something like "OpenGL" or "Direct3D".

If that doesn't help, open the dosboxDK.conf file in GOG Games\Dungeon Keeper Gold using a text editor such as Notepad. Scroll down to the [cpu] section and replace core, cputype and cycles so they look like this:

core=auto
cputype=auto
cycles=auto

Let me know if this helps.

try cycles=max