Okay, so let's say that after the League of Three Emperors breaks down, Germany sticks with Russia instead of Austria. Or maybe the secret parts of the Reassurance Treaty get revealed and Austria leaves Germany, who then officially allies with Russia. After that Austria then decides to ally with France. Things progress more or less as OTL and you end up with Serbia doing something to piss off Austria-Hungary.
You have a situation like this:
Germany, Russia, Serbia, Romania and Montenegro on one side.
France and Austria-Hungary on the other side.
Britain is neutral, but finds R+G intimidating so is leaning towards F+AH. They'll probably jump in if they think the balance of power or their interests are sufficiently threatened or if Belgium (or another similarly neutral country) is attacked.
Italy is more than happy to join G+R, but is waiting to see how the initial battles go before it jumps in - wouldn't want to join the losing side, now would it?
Bulgaria would probably join F+AH if they're sure they were winning, but is otherwise not going to risk its neck by getting involved.
The Ottomans are neutral, but they very well might jump in to try and annex some territory towards the end of the war, no matter which side is winning. However, if one of the factions makes a good offer they might join earlier.
The United States are still in full isolationist mode and the only way they're getting involved is if Britain does. In that case they might join their side later on, but it isn't a sure thing.
Japan would probably join whichever side Britain joins. If Britain stays neutral, however, then they might jump in to try and take some parts of Russia by themselves if they think they could get away with it.
Denmark is essentially a de fact vassal that, while being officially neutral, is guarding the straits against possible enemy vessels. If Britain joins and tries for a campaign in the Baltic like they said they would in OTL, Denmark will get officially dragged into the war.
Sweden is even more neutral than OTL. While they're generally pro-German, they're also anti-Russian which makes the prospect of joing G+R something of a mixed bag for them. If Britain goes for a Baltic campaign, however, then there's a good chance of them joining G+R.
Norway is generally pro-British, so if they enter the war there's a chance they'll join too - it's a slim chance, though. If Britain goes for a Baltic campaign, however, then the might have no choice but to get involved as either an ally of G+R or the more likely option of F+AH+B.
How do you think this is going to go down?