2408WFP OSD buttons and off switch freezing

I've just bought one of these monitors which I'm running as a second monitor from my Acer Aspire 8730 laptop. The laptop is running Vista 32 bit and has an nVidia 9300GS M graphics card. According to Device Manager I have up to date drivers for the monitor and the graphics card.

My problem is that the OSD buttons stop responding after a widely variable period of time. This can be a matter of a few seconds to quite a lot of minutes. In addition to this I find that the on/off button is also frozen.

I have done the self test which brings up the floating VGA input box. The trouble shooting section in the user guide mentions a dialogue box should come up during the test but it doesn't. I have also tried it on a different computer with the same result.

I'm assuming it is a fault and it will have to be returned, but was wondering if anyone has come across this before? On the other hand is it me? Have I done something wrong or missed something I should try?

Any help or advice would be appreciated.