Help ! Atari 400 problems / questions

Hi all

I have recently acquired an Atari 400 and have read some good things about the 8mbit multicart and SIOP2PC boards. Eventually I want to build a multicart with those great old games on it.

However, I have some problems with my machine. Hopefully somebody out there will know the answer !!

The machine is a 16k PAL (I live in the UK) 400. Upon startup I get the Atari Computer Memo Pad prompt. All appears fine.

However, cartridges do not appear to work. I have tried five, with the following symptoms.

1) Star Raiders. Black band at bottom of screen, pink screen for the remainder, with "missiles" coming towards me. Some of the keys in the instructions elicit a response from the computer but nothing like what the manual says it should do.

2) Lode Runner and Fight Night. Just black screen and nothing whatsoever happens.

3) Activision Kaboom. The title screen comes up and can toggle between 1 and 2 players. When hitting start lines flash down the screen, then explosions and then nothing else.

4) Basic cartridge. The cursor appears but all commands bring up syntax error messages.

I've a feeling my machine is either faulty or possibly a NTSC version (although a UK sticker is inside the cartridge slot). If the machine is faulty, what parts need replacing, could anybody help me with the parts or am I best waiting for a 400 to appear on ebay. Are Best Electronics of California a good supplier?

Turning to the 8 bit multicart, will it work on a 16k 400 or do I need a memory upgrade. I can source an 800 XL reasonably cheaply but I'd like to use the 400 due to the 4 joystick ports.

I appreciate any advices from any fellow Atari user.

Regards
Steve