Take the server down to the minimum to POST:
The minimum components to allow the PowerEdge™ 1900 to complete POST are:
System board
Processor (with heatsink) in socket 1
One stick of memory in slot 1
1 power supply
Control panel (to turn on system)
If you are still having the same error, replace the motherboard.
The 4400: xxxx error refers to one of the hard drives and is failing or has failed.
The 2900:xxxx error refers to a log entry and not an actual diagnostic code.
The PCI express error is pointing to a problem on the motherboard. Taking it down to the minimum to POST will eliminate the peripherals that aren't required to pass POST.
Regards,