I bought this game last night and played about an hour with nothing extra installed. Everything worked perfectly. However, I tried installing the mods this afternoon and the game would constantly crash to the desktop before the Sierra logo showed up. I figured I could uninstall everything and then reinstall just the game and everything would work just fine.
I was wrong. I still get the CTD. I noticed that the mod files were still in the \Arcanum directory, so I deleted that and tried reinstalling. It still crashes. Uninstalling with the GOG uninstaller and through control panel doesn't fix it either. I ran a registry cleaner thinking something was left behind and that didn't work either.
Restarts, reinstalls to other drives/directories doesn't work either. Any clues as to what I can do? Thanks!

What OS are you running? Is the game installed now or have you uninstalled it?
First try a system restore . . . Start, Programs, Accessories,System Tools, System Restore.
I DO NOT mean the manufacturers system restore (Dell, HP, Gateway etc) as I am referring to the MS Windows restore. Restore it to the day before you installed, saved me many times, I suggest you always create a restore point before installing games and Apps . . . I name them something to make it obvious what it is . . . like "Before Arcanum"

So that you know, save games from retail version are not compatible with Drogs patch so as patch readme says, don't even try to use them. Also use other mods with Drog's patches unless the other mod guarantees compatibility with Drog's latest patch.
Other than those if you have Vista/Win7 try running the Drog's patches as administrator (right click the file and click run as admin). Generally installing old games outside program files folder in Vista/Win7 as they don't tend to like the restrictions placed by UAC on that folder.
Thats all I can come up with right now.

Thanks for the tips. I'm running XP now (old laptop). I tried the restore point trick. We'll see if that works.

Good luck, if it is an old laptop you might not want to install the HR patch. Laptop integrated video cards are real picky. You might try updating to the latest video driver before you go any further, they can be difficult to locate as they are sometimes under integrated and sometimes not. . . =)
Edit : oh yeah . . .before installing after the restore, manually delete the Arcanum directory
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I have had a similar problem, except that after installing the mods the game will not even start. My hard drive light flashes on and off like it is reading but nothing happens.
I uninstalled the game but yet to install it.
Any ideas before I do?
Thanks

If I do a system restore , , I always manually delete any left over directories for the game or app. System restore does not delete any files or directories on the system it just restores the registry and system files to the state of the last restore point. If you reinstall with the old game directories still intact . . . the install program may not overwrite existing files so . . . I do manual cleanups to prevent using any of the old game files.
It appears that some systems with certain hardware . . . cannot support the mods and patches. I would do a cleanup, reinstall and see if it works without the mods. It may be that the mods, especially the high res patch may not be compatible with newer hardware.