Dashboard electric warnings haywire

Hi,

I have a 2000 w reg Fabia 1.4 petrol estate.

The dashboard has started to malfunction in the following ways:

- flashing red temp warning light (when starting from cold)
- fuel gauge suddenly drops to empty
- immobiliser light flashing (,car with key under it)
- occasional steering triangle warning light

They are all fairly random - sometimes go back to normal if I restart.

I've changed the battery but there is no improvement.

The only change I have made since buying is putting in a stereo.

Any ideas what this could be?

Thanks for your help,

Josh