RichAllen: This fucking game doesn't work on my system!
korell: Which one? MDK or MDK 2?
RichAllen: I have Windows 7 64 bit...
korell: Check the game pages. Both MDK and MDK 2 state compatibility for Windows XP and Vista. As such, compatibility with Windows 7 is not guaranteed.
That said, there are users who have got these games running on Windows 7 64-bit, but it will differ depending on your computer setup, so with no details as to the hardware you are running there can be no help at all other than the standard fixes which you may well have tried, such as:
1) Trying various compatibility modes
2) Disabling visual themes
3) Forcing it to run with only one CPU core
4) Installing outside of Program Files (x86) - I don't think the new GOG installers let you install there any more anyway
5) Install the full DirectX 9.0c redistributable
From there we start getting to different solutions, such as using ddraw wrappers in case it is an issue with the old DirectDraw, are your drivers up to date, disable anti-virus to see if that was interfering with the game.
Lastly, contact GOG support. If you bought the game then they are there to assist where possible. They will want a DXDiag report from your system, though, so that they can see if there are any known issues and possible solutions with any hardware you have.
If all else fails, there is a guide in these forums to get the first game running in DOSBox. It requires downloading the official patches to obtain the DOS executable for the game along with obtaining a DOS4GW.EXE and HMI driver files. This way, if you can run DOSBox (which you should be able to) then you can play MDK 1 in it's old DOS format. The guide is here:
http://www.gog.com/forum/mdk_series/how_to_restore_dos_functionality_for_mdk MDK 1.
I will try running the game in XP compatibility mode.