Dying orchid - please help!

[namford]

Hi all

I am a beginner and this is my problem:

Bought an orchid (regular looking sort) that had 2 stems of good flowers. The flowers lasted for a few months, it even grew more flowers and a new stem. then, no idea what changed but all the flowers dropped off and the stems began to shrivel, so cut them all back. Now the air-roots are all dried up and I think even the roots inside the pot are almost dried (I am watering every 10 days and feeding every 2-3 feeds). The pot is clear with holes at bottom. I let the bark dry out before re-watering.

Now, the leaves are turning purple too. Please help me rescue this little dude, or is it too late?

The orchid sits on my kitchen window sill. I live in London, UK. I've had it about 6 months now.

Any help gratefully received! Many thanks