Light steering and speedo failed & shock absorbers

Hi, hope someone can shed some light on this, I'm going to take the car into
a dealer tomorrow to take a look but thought someone might know what the
problem is.

I drive a 406 V6, R reg - coming home from work tonight, I'd driven about
half a mile, stopped at a set of lights, then pulled off, I can't remember
if it happened straight away, but driving around the roundabout the steering
became very light. I was able to control the car, but just wasn't a normal
steering feeling. Also I noticed that the speedo had failed and was stuck at
0. I drove a further 100 yards or so and the steering returned, the speedo
flicked a few times and came back to life. I'm assuming that since the
weight of the steering is governed by speed, the fact that it thought I was
doing 0 mph caused it to switch to light steering. Does anybody have an idea
what might have caused this, might it indicate a failing part, or an
electronic/sensor type issue. Where is the speed sensor located, I had all
shock absorbers replaced recently could something have come loose?

On the matter of shock absorbers, based on some reading in this group I
think what I actually had changed were the suspension dampers. I decided to
get this done because the ride had become very hard, teeth jangling bumps
sometimes when hitting potholes or lumps in the road. After the change I
have noticed this is not so severe, but now I feel almost every bump on the
road, is this to be expected, I would have thought these should get absorbed
better. I've had the car from about 21k miles (now 98k) and seem to remember
the ride being a whole lot better than this originally. I also notice that
it moves around more on the road, particularly the motorway, and sometimes
gets 'stuck' on white lines and lorry grooves, pulling the car away from the
direction I want to go in. Is there something else that I should get looked
at to improve ride quality, should I be concerned about the workmanship. Are
the pulling problems possibly due to the tyres having been changed around
and the tracking is now out, or whatever its called?

Thanks for reading
Simon