Dell Dimension 1100 Help

I have had this computer for a long time, a Dell Dimension 1100, which was used as a basic browsing computer when I was younger. About 4.5 years ago, I took it apart so I could use it for parts. Now, I want to rebuild it into a better computer then it was back in 2006. Sadly, when I went to put it all back together and put the parts I have got back in, it would turn on and show a steady Amber light. I looked on the service guide on Dell's website and it said that a device was malfunctioning or not installed correctly. I then did various swaps of the RAM I had leftover, didn't do anything. I took some RAM from another computer, nothing. I even took the CMOS battery out and reinserted it, nothing. I replaced it with another, nothing again. I changed the default processor (Intel Celeron D 2.53GHZ) and replaced it with a Intel Pentium 4 2.8GHz. The Pentium 4 got further then the Celeron, but it was still not working. If I plugged in any device, like the CD Drive or a HDD, the Amber light would start flashing constantly. My thought was the motherboard may have died, although the board was showing a green light on it. I'm currently looking at buying a new 1100 motherboard (I have one on my watch list on eBay). Would it even be worth it or should I buy a new Socket 478 motherboard? I don't really want to get rid of the computer, I do want to keep it original as possible.

Any help to fixing this problem would be appreciated. Thanks!