You have named a bunch of symptoms that I am not familiar with. I can suggest only that you follow all the standard procedures and patches. It is important that you descriibe your system thoroughly and explain what you have done.
Check first the sticky thread here about thief2 running on modern computers. That takes you through XP. Then search here and at TTLG for anything related to Windows 7. There were some recent posts here about windows 7 that contained useful information.
I am not sure what the premier patch is. There are several re-sellers of the game who may have their own patches. You need to make sure the patch is compatible with your original EXE.
One thing that may bite you is that some recent graphics cards cannot play the game without DDFIX, and DDFIX only works if you have the right version of a patched EXE to begin with. So, it is important to understand the origins of your EXE and its patches and to see if they are compatible with DDFIX. There is a thread at TTLG about DDFIX that may shed some light on this. There is a fair amount of homework to do concerning combinations of system properties and what to do about it.
In any case, read the FAQ's, etc., one of which tells you to post your system stats. Most important among these is the video card and its driver. Also post any modifications you have done per the sticky thread. For example, if setting affinity to 1 CPU, how and when did you do it.
"What we've got here is a failure to communicate", the warden (Strother Martin), Cool Hand Luke