Well,
-you swapped the cables ~ no difference
-you pulled out the power plug of your other receiver ~ no difference (so no power interference by possible 'standby LNB voltage' of that receiver)
that means that no power comes from your bedroom receiver to the splitter.
Have you checked that LNB power is turned on in the receiver menu, as suggested by
@st1 ?
Otherwise your cable has a DC blockage somewhere: some splitter or connection box that doesn't pass DC (but you don't have that?), or your cable has a bad contact (possibly the outer part of the cable not making good contact to the F-plug?).
So I would check the F-plugs, and maybe test continuance of the cable with a multimeter (or with light and battery).
BTW I find your setup with this splitter quite normal, when you accept the limitations in use (you cannot watch all programms, independantly, at both receivers).
With simultaneous use of both receivers, there might occur a control problem sometimes, due to non-synchronous 22kHz signal though. (There are ways to workaround this problem, but they are not 'nice' solutions: not really meant to be.)
That disadvantage doesn't happen with a priority switch as mentioned by
@Trust1 , though that could have the disadvantage of reduced signal on some frequencies at the slave receiver, with simultaneous use of both receivers.
But after the above tests: changing the splitter wouldn't solve your problem, I guess.
greetz,
A33