how to reassign which drive the computer uses for memory cards?

I stuck a compact flash memory card into my computer and it wouldn't see it.

Somewhere I saw that the computer sees memory cards as drive K.

It so happens that some time ago I set up a partition on the hard drive as K.

I went into Disk Management and changed the letter to R, restarted the computer. It now won't see any drive. Everything on the desktop seemed to work and I could access the internet, but whenever I tried to look at C or R it would say something like 'server failed', or 'cannot locate server'.

So I went back to Disk Management and changed the letter back to K and now everything works fine.

I have a number of programs located in K.

If I can I would rather re-assign which drive the computer uses for memory cards.

How can I do this?

(Win7, 64bit)

There is no fixed letter assigned to any volume (except for C for the active OS partition). The rest can be anything. But if you change the letters in 20/20 hindsight, you get the effects you have seen because you have broken the path to the data on the volume.

The memory card can be read by the printer, but is not being seen by the computer.