I also agree with Dagon's first paragraph. Then, since I don't know which game Omega is playing except that either is possible, I will assign 0.5 probability to each game, calculate expected utilities (reject -> $5000, accept -> $550) and reject.
For general form I will reject if k > 1/k + 1, which is the same as k*k - k - 1 > 0 or k > (1+sqrt(5))/2. Otherwise i will accept.
It seems like I'm missing something, though, because it's not clear why you chose these payoffs and not the ones that give some kind of nice answer.
Either is possible and no mention is made of how it's chosen (in fact, it's explicitly stated that the probability is not known), so why would you assign 50% rather than 0% to the chance of game A? If Omega mentioned a few irrelevant options (games C through K) which favored reject, but which it NEVER used (but you don't know that), would you change your acceptance?
The idea for this problem is gotten from dmytryl.
The payoffs only need be of the form: 1. $k*X (k: 1 < k) (X: 1 < X)
2. $X/k
3. $X
4. $0
If $1000 is irrelevant to you, then substitute for any enticing value of X, and replace $X with X utils. There is no diminishing returns on the utility you gain from the reward Omega gives you.
Do you have a strategy for a general form of this problem?