Hi Ewen Here is a tip I wrote for Win 98 which may help; Extreme Reinstall Win 98 This technique should be used if all other methods fail. Try to backup all data before reformating. If you cannot seem to resolve your problems with standard troubleshooting procedures you man need to go to 'Extremes', and do a complete* install. Uninstall all the drivers for all extra cards ( from Control Panel, Device Manager), sound, modem, CDR if it is in addition to the CD Rom, and extra hard drives if you have them. Shutdown, and remove or unplug all the 'extra devices'. Reformat, reinstall Windows, run scandisc, run defrag. Try running it without anything else plugged in. If it works ok then start adding devices one at a time, using the computer for a while after replacing each device. Then with each reinstall of device or software reboot 2 times, then run scandisc, run defrag. When the computer runs OK with the devices added back then start reinstalling application and programs. One at a time with test runs, including shutdown and reboot 2 times in between. This will be a very slow process but it may allow you to determine if there is a device, application, or program which causes the problem. ~~~ I hope this helps Mike ~ It is a good day if I learned something new. Editor MikesWhatsNews see a sample on my web page http://www3.telus.net/mikebike <mikeswhatsnews-subscribe@xxxxxxxxxxxxxxx> See my Anti-Virus pages ~ http://virusinfo.hackfix.org *********** REPLY SEPARATOR *********** On 29/08/2002 at 12:12 PM Ewen Howe wrote: Thanks very much, Jim and others! I trust all your suggestions may work, but this apears to be a strange problem. Further trials indicate that the A: prompt achieved from booting the Win98 disk is actual not working, it may move around different drives such as c:. d:, e: etc but none of those drives are virtually working. Thus, I am not able to use any of your strategies... I am describing again what had happened: I followed carefully the instruction of the new MB and assembled what I had on the old MB. After confirmation of very pieces again, I switched on the power, POST was OK and I was able to get into BIOS manu by pressing the Del key. After the POST, however, a message apreared saying 'In valid system disk, plaese remove it from the drive and hit any key' and the machine stops there not going any more... I made a trial boot using a set of 4 disks made from Win2000 CD as suggestted by Barry in previous message. This time I was allowed to install the Win2000 but the resulting OS did not work in full functionally with mouse failed and monitor worked in limited resolution (not sure other windows functionalities). This happened to my PC at home. I must work during daytime and I could only work on the problem when I get home in the evening after about 2 hours driving. So the progress is slow, please understand. The next trial I am planning now is to re-assamble again removing all unnecessary pieces to make it into a very basic PC with video card and FDD only, to see if it is due to the hardware incompatibility. Thanks again for your kinders. Ewen - Users can unsubscribe from this list by sending email to 24hoursupport-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field OR by logging into the Web interface at http://web.tampabay.rr.com/spider1/24hrsupport.htm.