Sometimes, I have had the problem with dust on the dock portion of the connector. If, after a longish period of no use dust gets in there. You might try blowing it out, off. a little moisture is not bad, if you have a can of compressed air to blow it off with quickly.

As well, the female side on the bottom of the lappy can get dirty and sometimes a bit corroded. Clean that off too.

The dock connector, IMHO is a weak link, especially with frequent connecting. I have often had the problem of connecting, and having it not properly seat, or connecting but not communication CONNECTED to the I/O on the dock or connector.

If you're looking for a dock of that type, try thinkpads.com forums, for great marketplace, or pm me, I've got a couple sitting around.