Sverre: Please take a good hard look at your bore, it may be pretty rough and needs a good lapping. There isn't any real good reason why that rifle shouldn't shoot. You amy also need to slug your bore to check the diameter. Some of the Marlin shooters have found their 44 magnum bores to be very oversized and you may have a similar problem.
Also, you didn't mention if it was scoped or if you were using open sights. If your sights are open and factory, please check to make certain they are tight to the barrel. If the front sight happens to be a tad loose it will throw your groups off badly. If the rifle is scoped, check the tightness of all screws, etc., then check the scope as it may have gone south on ya.
If all else fails and she still won't shoot for you but you really want a 94 in 44 mag, send it back to Winchester and have them fix it for you. I recommend that as I had serious problems with a Black Shadow I once bought and the thing went back to the factory twice before I even got it to the range. Now, a bore lapping and 300 rounds later I wouldn't get rid of it for a tall blonde (lol). HTH. Mikey.