Repair ASUS Z53t (F3TC), POST error

Hi all,

A friend gave up on his ASUS Z53t laptop a while ago (maybe a couple of years back) because it stopped booting. This is a European model from 2006/2007 that uses the F3TC motherboard and the general build is essentially the same as the F3 series. My friend says the battery stopped working, meaning the machine wouldn't start with only the battery despite charging. "Who needs a battery," he decided, and just ran it from the external power supply with the battery out. After several weeks, the machine wouldn't boot anymore. Now he's passed it on to me and it's not urgent but I'd like to use it in the office, and yes it needs some attention.

Boot error
Here's what happens when I push the power button with the external power supply plugged in, but no battery or hard-drive. The power LED comes on, the background lighting of the screen shifts, the optical drive makes a brief sound, and then two faintly audible beeps are issued. The fans do not run, and nothing appears on the screen. So essentially, the POST fails.

Initial diagnosis
This board uses an AMIBIOS, and two short beeps under AMI's beep code means a failure in the parity circuit ( pcguide, bioscentral, computerhope). This should be fairly universal, but it's possible that ASUS modifies the BIOS code. According to pcguide.com, this could mean a problem with the system memory, or with the mainboard. It apparently is also possible that something is wrong with the CMOS memory; I read on a forum that someone reset the BIOS or changed the CMOS battery and this resolved similar boot errors. It doesn't make sense to me that a low CMOS battery would suddenly cause the POST to fail, unless the CMOS memory got corrupted. I figure it's worth a try. I'm also not sure whether there's a connection to having run it without the main battery.

First attempt at repair
I've witnessed a pro disassemble, repair, and reassemble a notebook before, when a Dell technician repaired my M1330. Quite intimidating. I build my own desktops, but have never worked on notebooks. Undaunted, I removed the rear panel to have a look. I can easily access the RAM modules, so I tried swapping them and inserting just one at a time. This didn't solve anything, although I'm not sure which is the first slot. I'll try some different configurations, but don't expect that to be the solution.

Outlook
Web searches have failed to turn up other cases with F3/Z53 models and the same problem. This includes sites and forums in German, where the Z53t designation appears to be most common. To me a logical next step would be to try resetting the BIOS by removing or replacing the CMOS battery. I've found out it's located in an almost-but-not-quite accessible area, and seems to require removing the entire bottom part of the case. Before I go to any such lengths, I'd like to hear some opinions on how to find out what the problem could be and what else to try. I can post photos and make tests, although I'm stressed for time so progress will be slow.

In case I do want to take it apart, ASUS is hardly helpful and disassembly guides for the Z53 and F3 series are nowhere to be found, not even at repair4laptop.org or in the ASUS Info Booth. If I can go by the F3 similarity, however, I've found guides of a sort on this forum:
Disassembly guide for F3SV
Disassembly guide for F3 series
If it comes to disassembly, I'd need help but will want to proceed slowly and take lots of pictures, so we could create a more thorough guide for this model.

Thanks,
Mike