What is wrong with my Cymbidium?

[supersheep]

I'm hoping someone can help me save my Cymbidium, as I'm not sure what's wrong with it. I've never had a Cymbidium before and this was given to me as a present. It had three connected pseudo-bulbs, all with green shoots, but very few roots when I was given it. It wasn't in any medium, so I put it in a clear pot with holes and used some orchid potting mixture (the make was Orchid Focus, mainly bark chippings). I put it on a windowsill that doesn't get a lot of direct sunlight, but there's not a lot of choice in my house. Another window gets a lot of sunshine and I think this may be too much (it killed one of my Phalaenopsis last year during an unexpected heat wave)

This Cymbidium didn't do anything for a couple of months, but then I noticed the shoots on one bulb were going all brown - from the outside in. I feared an infection, so I removed this pseudo-bulb. The rest of the plant seemed fine, but then the brown seemed to spread and now the other two pseudo-bulbs are growing brown. A few of the leaves have gone brown too and snapped off. The pseudo-bulbs are still firm to the touch though.

I've attached a few pictures to show what I mean.

Does anyone know what's wrong with it and what I can do to help.