I've got a TomTom Start 20 and it up until yesterday it was receiving a signal perfectly fine.

This morning I went to use it - nothing all day. Tried resetting the unit via the menu and still nothing.

Borrowed the work one again and had no problem except coming back on the A30 from Cornwall into Devon I did notice the borrowed unit going a bit berzerk as it was thinking I was driving through fields. Every time it hit a road coming off the A30 which I was actually traveling on you could see the unit re-calculate the route.

The weather here has been very bad all day, very grey overcast, plenty of rain and fairly windy so not sure if that has anything to do with it.

My Start 20 has been stored in the box it came in and has never been subjected to shock and has been looked after very well.

Any ideas?

Have you tried updating the quickfix data through Home?

ALL FIXED!

[Please Register or Login to download file]

There's a fault with some third party chip(s) - I downloaded the update and everything is now working perfectly fine.

Ah, you simply had not installed the update half of the world was talking about...
Sometimes it is good to check with Home/MyTT ;)