Will not boot discovery

Hi all would be most grateful of any help/suggestions with my problem.

Have a Discovery P4 notebook 8175 which was working fine then went to boot up and received message cmos checksum invalid==run SCU after trying to install networkwork card.

Since have not really been able to boot. will boot through bios sometimes first running memory test that halts at message F2 to reboot or Del to default but tapping keys gets no results just hangs.
Checked hard drive on another laptop which booted OK. My battery will not hold a charge so have recently only been using charger but up until now all has worked fine.

Have tried reseating memory, trying to boot without HD, DVD or battery or one or other. Have read that it may be cmos battery ?.

Any suggestions

Maxman51

I think it is the cmos battery for sure. Basically what I think is happening is that due to lack of charge in the battery your bios settings are not being retained hence the message constantly appearing. The battery may or may not be easily replaceable, I don't have a lot of experience with laptops but I doubt it will be an easy job :(

I presume it's a Mesh laptop? Tried searching the web for the user guide but no joy so far but it should be fairly straightforward to replace the cmos battery - it's just knowing where it is and how to get to it!