Laptop problem--stumped. Hard drive? RAM? Ghost in the machine?

Hi all,

My girlfriend has an IBM T42 laptop that has been giving me some grief recently. I've been unable to figure out what's going on with it. It all started when she booted it up and got a "Disk read error has occurred" error. I've tried a whole bunch of things, detailed below, and while it initially seemed to be a simple dead HDD, I'm starting to worry that there's something else at the root of all this.

Details on what I've tried:

• Started with "A Disk Read Error Has Occurred"

• Booted to WinXP rescue disk and reinstalled MBR and ran CHKDSK. Machine still booted to Disk Read Error.

• Tried putting into her laptop the HDD from my working laptop. With this HDD, it got to the WinXP loading screen before I killed the bootup since I have a diff model laptop and didn't want windows to start autodetecting/installing her device drivers

• Tried reinstalling Windows, but the disk format locks at ~36%.

• At this point, it seemed to me to be a dead HDD. So she could use the machine while I got a new drive, I put Mint Linux Live CD on a bootable USB disk and booted to this

• Machine booted fine to Mint at first, but was flaky. It hard locked once or twice, and several times, when rebooting, it would not post at all

• Removed USB disk to see if this was why machine was not posting--no dice, machine still didn't post

• Start thinking there is something at work here bigger than just the HDD.

• Pull the extra stick of RAM from the machine (addon stick that I installed a few months ago, not the OEM stick). Starts posting.

• Repeat this test a couple of times: RAM in, it won't post. RAM out, it posts fine. Do this several times. Perhaps the RAM is bad too?

• I put her stick of RAM into my laptop and boot to Memtest. Run memtest overnight, no errors. Interesting.

• Put the RAM back into her machine the next morning. This time, posts fine. WTF?

So now I'm getting stumped. The HDD definitely appears to be dead, which is fine, but I don't get why the RAM is SOMETIMES making her machine act flaky, but not all the time--and why no errors show up on memtest. Furthermore, why is all of this happening at the same time?

I'm starting to get worried that there is something else wrong with the machine that is causing all of this to happen as symptoms, rather than as the actual problem itself. Perhaps bad mobo, chipset, I don't know. Grasping at straws at this point.

Any thoughts? Any help or suggestions are much appreciated, I'm getting stumped here.

Also, let me know if there is any other information that anyone needs.

Thanks again!

I had a T43 that did this, but it was still under warranty. Turns out the motherboard needed to be replaced.

It's about 5 years old, so that could certainly be the issue. Would a bad CMOS battery cause these kind of flaky symptoms though?