My tomtom wont work

I am new to this forum so please be gentle with me. I bought a tomtom from a second hand shop, I was told that the maps were of the UK and Europe. I am unable to find any streets on this and it wont accept postcodes. I keep getting that is unable to tske me directly there. I made a back up of this and tried to install the UK map on it instead but I am tole that there is at least one file missing. Tomtom home doesn't pick up this tomtom and the pc shows as a removavle disc. I dont know how to reinstall the map or how to find streets which was the point of getting this. I was tolld this was a 910 but cant get it working properly. How do I get missing files and maps? The map is prm file but the ones i am getting are different to this, they are pna files and midi.