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I have Two Dell Optiplex 755, one is newer condition than the other, both working properly. I took the hard drive from the older Dell and swapped it with the hard drive in the newer Dell, because I want to use the newer Dell. But, when it starts booting up, at the Windows XP splash screen, it reboots and then repeats the cycle in a loop.

Just to check, I swapped the HDDs back again, and both boots up normally. I don't understand why. Both Dells are the same model, with manufactured date within a few months of each other, with the same type of CPU, graphics, RAM, hard drive, etc. Does anyone know how I can fix the looping reboot problem?

Both machines are in AHCI mode.

If the auto-reboot is disable, there is a blue screen error with a cryptic number.

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Are both machines in AHCI mode? Using the same AHCI driver? – Shinrai Oct 27 '11 at 22:19
If you disable the auto-reboot on error, is there a blue screen error reported? – Ƭᴇcʜιᴇ007 Oct 27 '11 at 22:45
Thanks for your replies. Yes, both machines are in AHCI mode. And, yes, if the auto-reboot is disable, there is a blue screen error with a cryptic number. – Darcus Oct 28 '11 at 21:56
@Darcus: Do you mean a Blue Screen of Death? What cryptic number do you refer to? – Tom Wijsman Nov 1 '11 at 15:02

There are still minor differences (i.e. serial numbers, MAC address, etc) in the 'fingerprint' the Windows activator looks at. It sees it as a different machine, then thinks you're trying to pirate.

Sometimes, you can just boot in to Safe Mode, and all is fine. If not, a repair install sometimes works. The last step is to wipe and reload. Do you still have your XP CD?

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If the WGA kicks in and deactivates Windows it never disables the machine completely. It simply limits your usages and nags you to "make it genuine". :) – Ƭᴇcʜιᴇ007 Oct 27 '11 at 22:46
Not always the WGA doing it. The HAL could be different enough as well – Canadian Luke Oct 27 '11 at 23:02
You mentioned the "activator" and the MAC and serial numbers, so I figured you were exclusively speaking of WGA. :) The HAL is exactly what makes Windows portable; it doesn't change. I'll stop hassling you now. :) – Ƭᴇcʜιᴇ007 Oct 27 '11 at 23:08
/face palm. You're right, I said activator.... – Canadian Luke Oct 27 '11 at 23:11
It also fails to boot into Safe Mode; it just also reboots in a loop. I've tested with re-installing WXP with "Repair", after which it still reboots in a loop, but when installing a fresh new WXP (on a spare HDD), it boots into Windows normally. But I want to avoid a new Windows installation, even if I could transfer documents and settings, because I want to preserve a long legacy of apps installed since Windows 3.1 for which I no longer have the original installers. – Darcus Oct 28 '11 at 22:06

Motherboard hardware is too different, do a XP repair Install. You may have to install drivers after the repair is done, go to Dell and punch in the service tag for the newer 755 to download them.

See "Replace a Failed Motherboard" section of this article for instructions on how to repair

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It's unusual for the motherboards to be so different in two machines of the same model with the same type of CPU, RAM, video, etc., and manufactured within s few months of each other. As I mentioned above, I tried the repair install with the same looping reboot as a result, so even if there are newer drivers for the newer machine (there aren't), I wouldn't be able to install them. – Darcus Oct 28 '11 at 22:11
Repair install removes all drivers and installs the one's available on the XP disc, which won't be much, after the repair you will have to install drivers again. Makes me wonder if it is some 3rd party driver that won't load causing the loop. – Moab Oct 29 '11 at 14:45

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