SC 1435 with random crashes.

[Rahul]

I have a PowerEdge SC 1435 that has a strange problem. We bought about 23 of
these for a cluster and machines have been failing in a somewhat random manner
in a peculiar way:

(1) Screen is blank. Front blue indicator turns steady orange.

(2) Cannot get it to reboot by pressing (or keeping depressed) the power button

(3) only way to reboot is to cycle the power.

(4) After reboot machine works fine again , till after a few days same failure.

Ran the dset and diagnostic CD but nothing relevant. 

Any tips what could be the faulty component? Or debug ideas? Right now I'm
totally lost! Hardware / software? CPU / Motherboard / Power supply?

Anoybody knows what exactly makes the indicator LED turn steady orange from its
normal blue state? This is not one of the 4 numbered LEDs but the one to their
right.

Any suggestions are appreciated!