Yes I did check last week, no errors, and haven't removed anything.
Try right click on jk2mp.exe and click properties->Compatibility->Run in Win 98 mode. Click ok and apply and try again. If that doesnt work go back to the compatibility menu and choose 256 colors and try. These have worked for friends of mine with the jk2mp.exe stopping at "dectecting cpu"
I cannot say for sure that this will fix it for you, but its worth a try. :)
Whoo! It worked thanks for your help S.T.A.L.K.E.R and TacoPie.
Glad to hear it :)
Also, which version of JK2 do you have ?