|Failing power supplies are common. |
Failing mboards are not.
I'm assuming the system that won't boot is the one with the AN35N Ultra mboard, AND that you DID NOT change the ram installed in that mboard from the ram that worked fine before.
It's a lot more likely the AN35N Ultra system's PS is no good than the AN35N Ultra mboard is no good.
There's probably nothing wrong with the 12v connector or it's wiring, but the PS may be failing.
Failing power supplies are common and can cause your symptoms.
Check your PS.
They often partially work, fans and hard drives may spin, leds may come on, yet you may get no video and the mboard will not boot all the way.
See response 4 in this:
If it is failing, you can usually replace it with any decent standard sized standard ATX PS with the same capacity or greater.
Standard (PS/2) power supply size - 86mm high, 150mm wide, 140mm deep, or 3 3/8" h x 5 7/8" w x 5 1/2" d , or very close to that, though the depth can be more or less for some PSs.
Don't buy an el-cheapo PS.
See response 3 in this:
If you want to confirm whether or not your problem is the PS before you buy one, try a known working used one.
If you have a spare PS that has the ATX 12V plug (two black, two yellow wires), or if you can borrow one, try that with the Shuttle AN35N Ultra.
(Most PSs that have a 24 pin main connector have one that can be used for both 20 and 24 pin sockets - the 4 pin connector part clips onto or slides onto the 20 pin one and is removable.)
Or you could use a wiring adapter with a PS that does not have the ATX 12V plug to provide the ATX 12V plug.
Either buy one, or if you have the pieces laying around you could make one.....
If you have a dead fan that has the male and female 4 pin hard drive size molex connector, and a dead PS that has the ATX 12V plug, you can make an adapter - connect the male molex connector's black wires to the black wires of the 12v plug, and the male molex connector's yellow wire to the two yellow wires of the 12v plug.
Can a bad power supply cause a corrupted bios?
A failing power supply can damage the mboard and/or anything connected to the mboard.
However, I've never seen or heard of an instance of where the mboard still worked somewhat and you could get into the bios to even check to see if it's corrupted. If a PS has damaged the board, you often can't get into the bios in any case, and you often have no video.
If you DID change the ram installed in the AN35N Ultra from that that worked fine previously.....
Ram that works in another mboard , or any ram you buy or have lying around, may not work properly, or sometimes, not at all - even if it physically fits and is the right overall type (e.g. SDram, DDR, DDR2, etc.; PCxxxx, xxx mhz) for your mboard. In the worst cases of incompatibilty your mboard WILL NOT BOOT all the way with it installed, and the mboard may not even beep - the ram has to be compatible with the mboard's main chipset, or in the case of recent mboards, compatible with the memory controller built into the cpu.
If you still have the ram that was installed when the system worked fine, try installing just that ram.
See response 5 in this for some info about ram compatibilty, and some places where you can find out what will work in your mboard for sure:
Correction to that:
It is easy to test for incompatible ram that has caused your mboard to fail to boot.
Make sure you have a speaker or speakers or the equivalent connected to the mboard so you can hear mboard beeps (see your mboard manual if you need to).
Remove the AC power to the case/power supply.
Remove all the ram.
Restore AC power.
Try to boot.
If nothing else is wrong, you will get no video but you will hear a pattern of beeps that indicate no ram is installed, or a ram problem.
E.g. for an Award bios or a bios based on one, that's often a beep of about a half second, silence for a half second, a beep of about a half second, silence for a half second, continuously.