GA EP45-UD3P restarts when trying to load windows

I might be wrong, but your PSU might be a bit under powered?
The CPU has to start doing some work, as well as the HDD when Windoze starts to load, so that would increase the power consumption.

On the other hand, Windows might not like your new system. What are the specs of the old system?

Maybe I'll try a different PSU just to see - would be an easy fix if that;s the problem. I was trying to find the recommended minimum PSU for the MB but couldn't find it in the gigabyte documentation.

Curious why you think Windows doesn't like the new system. Shouldn't windows work on any system (or at least try to start up)? Old system was ASUS P4S8X with a P4 2.4 Ghz, 512 RAM. Same PSU.

BTW - I'll occasionally get the option to start in safe mode, etc. The only thing that actually looks like it does anything before it restarts is safe mode with command prompt - it will scroll through a page or so of commands, pause, then restart. Just in case that helps...

Just so I'm clear, you're using a hard drive from an old computer with Windows already installed on it, inside the new computer without changing anything?

Unless you have compatible chipsets that use similar/the same IDE Controller chips, it will never boot in the new PC.

What you'll have to do is put in your Windows CD, boot from it. Press Enter as if you're going to install Windows XP from fresh but then chose R for a repair install.

Don't press R on the first screen or you end up in the recovery console which is no use to most people.

On a side note, why is everyone here obsessed with PSU's being underpowered and other bizarre entirely random pieces of hardware that might cause a crash every second Tuesday when its a blue moon and theres rain over the Sahara?

You're right, but it's not as if I'm wrong?
I saw something similar when I was putting my new system together on a rubbish 400W PSU. And PSUs are rated for a reason.

I'll try the repair install. What I did previously was from the recovery console, but I'll try it the way you suggested. I assumed that I could just move the drive to the new system and that it would at least boot and then I would likely have to reactivate XP - I didn't realize it wouldn't even boot.

OK - so I can get a little farther now. I started the repair installation - it copied all of the setup files, The computer restarted. I allowed it to start by the hard drive. I now get a Windows XP Home screen - the green bar moves across a few times, then the keyboard lights blink, the display has a quick blue screen, and it restarts and does the same thing. Why can I not get past the XP screen???

Don't do a repair, its trying to repair the old inatallation to the original old config! re-boot off the CD, press enter to install windows, F8 etc. It will say it has found an existing windows, do you want to repair - don't reapir, carry on as if you are installing a fresh windows. Where you choose the hard-drive select your hard disk - it will say that there is already a copy of windows there - proceed and select to install to your old windows directory C:\Windows. It will install a fresh copy over the top of your old windows and will detect all your new hardware during the process but will keep all your programs and files.
You have to do this every time you make a significant hardware change like moving from an AMD chip to Intel, or single core to dual core. That said though it is highly recommended to perform a true fresh install - i.e. format and then a clean install - every 12 months or so as windows degrades with use.

If you do this, do the programs and drivers (that don't need to change) stay installed. Installed as in working/on your start menu?

It re-installs windows, but I think in the process it will not overwrite certain historic files it finds, which means that all your non-windows files will reamain untouched. The vast majority of your installed programs will appear in the new start menu. Those that do not are still in the programs files directory and will still work if you run the exe, you just have to create shortcuts for them. You will have to re-intall all your hardware drivers if you use this method.
Its not ideal, but it is the only way you can keep an old install working after you have made a major hardware change to the system as the core Widows files need to be re-written and not repaired.

It re-installs windows, but I think in the process it will not overwrite certain historic Windows files it finds, so the vast majority of your installed programs will appear in the new start menu. Those that do not are still in the programs files directory and will still work if you run the .exe, you just have to create shortcuts for them. You will have to re-install many of your hardware drivers if you use this method, although Windows may detect some of them, and of course there will be the remanants of your old drivers in there too.
Its not ideal, but it is the only way you can keep an old install form another system working as the core Windows files need to be re-written and not repaired. Otherwise the only other option is a format and fresh install.

The reason it won't load is because the old and new computers were so different, so do a repair or fresh install of windows.
However I would still question whether your 350w psu will be up to the task of running the computer at full load.
I have the same mobo, an e8400, 4850 and 2gb of ram with a ide hd and the psu calculators I have used tell me full load is between 300 and 350 for my computer. Not sure what gpu you have but I know a q6600 uses more power than mine and you have twice as much ram. So I'd look into a new power supply as well if i was you.

Thanks everyone. I was so tired / frustrated (and didn't have acces to the internet to read your recent replies) that I found an old 30G drive and installed windows fresh on that. Things now boot fine, but the graphics card was freezing. After reading the recs on the card, it recommends 18A on the 12V. Mine was only 15A. So I got a 450W with 32A on 12V and all is good. So, new windows, new PSU, 6 hours of BS, and so-far-so good. I haven't stressed it yet, but will try that soon. First have to re-install programs, patches, etc etc..... Thanks again.

Question about your setup... I am looking to get the same mobo, and I read that some people had problems with it recognizing only one of two 2MB sticks. You installed yours in slots 1 and 3. Any reason? I'm also looking at Crucial 2 x 2 MB.