The problem you has it I think can be for a modification on your instalation. To solve this you need a "CLEAN" Instalation of your Game.
1.- backup your save games
2.- Uninstall it, Check it there is a remanent archive(delete it if exist).
3.- Install it again.
4.- Install the patch.
6.- Copy your save games.
if you have the old installer "setup_one_unit_whole_blood.exe" I recommended to you download the newest version
"setup_one_unit_whole_blood_18.104.22.168.exe", only go to your gog adcount and download it again.
Teoricaly should fix the problem. :)
Ok we go Step by Step
1.- go where you installed the game and find "OUWB.BAT"
2.- Right click, and go to "edit"
3.- localize an replace the next lines (all of them) "BLOOD.EXE" to "BMOUSE.EXE LAUNCH BLOOD.EXE"
and "CRYPTIC.EXE" to "BMOUSE.EXE LAUNCH CRYPTIC.EXE"
5.- then save it
6.- and find on your directory "Blood.cfg"
7.- find the next line "ExternalFilename = "EXTERNAL.EXE" to ExternalFilename = "BMOUSE.EXE"
8.- remember to press "U" to activate Mouse look.
I have never Use it, I`m a completely "old" Gamer I usually play this classic Whit "Keyboard only" like other games before half-life. but I think can help you whit this. :D
comment it any further questions, I will put more attention to this post.