Tsjoert

In need of a simple and cheap navigation solution, I bought an iPAQ 1710 TomTom Navigation Pack (which comes with a car kit, TomTom 4.40 software and a TomTom wired GPS mouse).
The TomTom wired GPS receiver has real difficulty in acquiring a lock. It ususally takes more than 20 minutes when the car is parked (engine running for power) and while driving it's almost impossible to get a lock. Once a lock is acquired, the receiver also has great difficulty at keeping it while driving. However there's always 4 or more statelites with good visibility according to the GPS status menu of TomTom Navigator. Is something wrong with the receiver? Or can this be a software issue?
I contacted TomTom support a while ago, but apart from an automatic e-mail with a reference to the FAQ on their site, I didn't receive an answer up till now.