Intermittent Boot Failure
 

I have a roughly 3-year old PC that I put together from parts (listed below) that has been running great with various flavors of Linux as the sole operating system. It is currently running Ubuntu 10.4. A couple of months ago, it started to have intermittent problems booting. The machine will hang before it gets to the Ubuntu "boot" screen with the dots that show progress as the machine boots. If I look at the power on messages from the BIOS, it fails at different points in the process - sometimes during the memory test, sometimes during the search for IDE drives. It fails about 2 out of every 5 attempts to boot. It sometimes takes 2-3 tries at booting before it actually works. Sometimes when it does boot, the Ethernet jack doesn't work and I see errors in syslog about there not being a carrier.

There are no syslog entries when the machine does not boot.

The machine is plugged into a UPS. The UPS indicates that it is running at 13% of capacity at 123V/60Hz. I'm in the US.

Once the machine boots normally, it will stay up without issues for days.

I've checked the 4GB of RAM (I added 2GB to the original 2GB several months ago) using the memory testing application on the System Rescue CD and no errors were found.

I've replaced the motherboard battery, which seemed to help for a few weeks, but then the problem returned.

I've checked the hard drive for errors using the SMART diagnostics tool in System -> Administration -> Disk Utility and buy running fsck.

The interior of the case is not very dusty and all the fans appear to be working.

Are there things I can do to investigate and fix this issue other than starting to replace components - starting with the motherboard and the power supply?

Any advice would be greatly appreciated.

The parts of the machine:

CPU INTEL|C2D E6850 3G 65N 4M R - Retail (Qty=1, Price=$279.99)
CASE ANTEC|P180B BLACK RT - Retail (Qty=1, Price=$114.99)
MB GIGABYTE GA-P35-DS3L P35+ICH9 - Retail (Qty=1, Price=$111.99)
VGA EVGA 256-P2-N751-TR 8600GT 256M - Retail (Qty=1, Price=$109.99)
PSU ANTEC|TP3-550 RT - Retail (Qty=1, Price=$89.99)
MEM 1Gx2|CRUCIAL BL2KIT12864AA804 R - Retail (Qty=1, Price=$94.99)
HD 320G|WD 7K 16M SATA2 WD3200AAKS - OEM (Qty=1, Price=$79.99)
DVD BURN SAMSUNG|SH-S203B % - OEM (Qty=1, Price=$29.99)

Nope, it is time to elimminate components. You can try unplugging components and pulling andy PCI cards except for the video card one at a time. However my first guess would be the PSU or maybe the motherboard (could be some capacitors going bad).

unexpected result.
 

Based on Michaelk's suggestion, I started disconnecting components of the system to see if that helped. After disconnecting the DVD burner, the machine started to boot reliably.

I'm surprised by this, but pleasantly so, this is a quick $30 fix, not the very tedious $90 fix to replace the motherboard.