Here is a really cool feature of the AmigaOne XE/G4 and it helped me troubleshoot and fix mine. This takes all the guessing out of why it is not booting. I hear other AmigaOnes have this feature as well, however, I can't say for sure.
Connect a null modem cable to COM 1 (left port) and then use a terminal program. I used Teraterm it is free on the net. I also used a USB to 9 pin serial dongle. Set the serial to 115200, 8 bits, no parity, 1 stop bit. If you don't know how to do this and know a Cisco guy, we do this all the time to access routers and switches.
This is the output of my XE/G4. I was getting the "black screen of death" and it was failing at the memory check (1024 Line). I replaced the memory and I was back in business.
It seems like when I let the Amigaone sit for a few months, it won't boot and I have to reseat the CPU module. However, this was not the case this time. I hear about replacing the 2032 coin battery but that has never fixed mine. I was looking on YouTube and there was a guy that baked his CPU module in the oven to resolder all the connections. In his video it did fix his BOD. I would only use this as a last ditch effort because when the solder melts in the oven, your components can move or fall off.
This is what is should look like with 1 Gig of Ram in bank 0.
U-Boot 1.1.1 (Mar 3 2005 - 16:42:53), Build: 03/03/05
CPU: MPC7455 v2.1 @ 800 MHz
Board: AmigaOne
DRAM:
Information for SIMM bank 0:
Number of banks: 2
Number of row addresses: 13
Number of coumns addresses: 11
SIMM is registered
Supported burst lenghts: 8 4 2 1 PAGE
Supported CAS latencies: CAS 3 CAS 2
RAS to CAS latency: 3
Precharge latency: 3
SDRAM highest CAS latency: 750
SDRAM 2nd highest CAS latency: 1000
SDRAM data width: 4
Auto Refresh supported
Refresh time: 1042 clocks
Bank 0 size: 512 MB
Bank 1 size: 512 MB
Slot 1: vacant
DIMM0_B0_SCR0 = 0x00ff9f00
DIMM0_B1_SCR0 = 0x00ff9f00
DIMM0_B2_SCR0 = 0x007f9f00
DIMM0_B3_SCR0 = 0x007f9f00
Using CAS 3 (slow)
DRAM_GCR0 = 0x00550800
Refresh set to 2083 clocks, auto refresh on
DRAM_REFRESH0 = 0x00019823
Mode bank 0: 0x00008032
Mode bank 1: 0x00008032
1024 MB <----------------------MINE WAS STOPPING HERE!
FLASH: 0 kB
VGA: 0 ..
In: serial
Out: serial
Err: serial
