Help! some time ago I bought a 256MB memory upgrade for my laptop, taking the total from 256MB to 512MB. After fitting the memory, the laptop won't boot properly as described below. Can you help me resolve the problem?

The laptop is a Dell Inspiron 2500 running Windows ME with flash BIOS version R52472. It doesn't have any other operating systems or non-standard boot managers installed. The memory is a 256MB stick from Crucial (BG111MQ.7X CT32M64S4W8E.16FG), as recommended by the Crucial online memory selector.

With the extra memory installed, when I turn the laptop on the message 'Operating System not found' appears after the BIOS initialisation where I would normally expect to see the Windows ME splash screen. The BIOS setup screen shows that the BIOS has detected the extra memory.

The system will boot successfully if I put a bootable Windows ME installation CD in the CD drive, and select 'boot from Hard Disk' from the menu offered by the CD boot manager. Having booted like this the system works fine; there are no device conflicts, the system property sheet shows the extra memory and everything behaves as normal. I can also see from the System Monitor application that it is making use of the extra memory.

My tentative conclusion is that the problem is associated with either the Master Boot Record on the disk drive, or the contents of the boot sector.

I've discovered that I can effect a temporary repair by booting from a startup floppy disk, and running 'FDISK/MBR' and 'SYS C:'. It will then boot from the hard disk as normal once, but at the next reboot the 'Operating System not found' error comes back. This seems to suggest that the MBR and/or boot sector are being damaged each time the system boots with the extra memory in.

If I take the extra memory out I still get the 'Operating System not found' error, but if I run 'FDISK/MBR' and 'SYS C:' it boots successfully and the problem doesn't come back (as long as I leave the extra memory out!).

If I remove the original 256MB memory card and fit the new one in its place, it works fine. I also tried swapping the old and new memory cards over but this still leads to the 'Operating System not found' error. In other words, the two memory cards seem to behave identically, and the problems occurs whenever I have both fitted.

I've run scandisk, the Dell hardware diagnostic tests, and various brands of antivirus scanners. None of these have shown any faults with the disk, RAM, processor etc.

Do you have any suggestion to resolve this problem? I do need the extra memory, but it's no good unless I can get the PC to boot!

Thanks for reading!