I'm needing some help with a friends PC. A while ago, he called me regarding a message he got on his PC, which he wasn't able to note down fully before his PC powered down. Something about a BIOS checksum error.
Anyway, I took it to work (work in a office IT department) and myself and a few colleagues had a look it over the course of a few days and this is what we've found.
First of all, the PC wasn't posting or anything. No beep codes, no display...nothing. So we tried some simple things first. Swapped the video card and got the same nothing. Swapped the RAM and got the same nothing.
We came to the conclusion it must be the Foxconn n15235 motherboard and so we ordered a new one. Once it arrived we swapped out the motherboard and tried it again. This time we got no display and continuous long beeps. The manual for the motherboard indicates this to be a RAM problem, but swapping the RAM resulted in the same problem. It was at this point we concluded that it was the CPU, an Intel Q8200 Quad Core, but without ordering up a new CPU we got a Socket 775 CPU out of an office PC and tested it.
Success, we have a post beep and display and the system looking for a boot device. Testing his CPU in an office PC (HP dc7700) which we know was working just resulted in a red light on motherboard and a lot of angry beeps. So myself and my team concluded it was the CPU and so I ordered him a new one.
Anyway it arrived this morning and you know doubt have guessed already from the very existence of this thread that something is wrong. Indeed it seems to be the case. The new CPU and the new motherboard are now installed and we get the same no display and continuous long beeps, or at the very least, I got that once. Now whenever I power it on, I get nothing. No display and no beep codes. The same problem we first had before buying anything new. Even removing the battery and clearing the CMOS jumper results in the same no display and no beep codes when I power it on.
So, new CPU and new motherboard and nothing. We know the RAM is fine and during all the testing, all non-essentially hardware (HDD, DVD, USB etc) haven't been plugged in. We've even tried a new PSU (when the PC was at the office during the week - I've not been able to test a different PSU here at home).
I'm getting really frustrated with this PC as I've now advised my friend to spend £150 on parts and it's still not working.
You may have neglected the most important item, the power supply. It may be getting old and running at a marginal level. I always change mine with a new board if it's over three years old. You won't need an expensive one, but I recommend one of these brands: antec, corsair, seasonic, enermax, or ocz. The better brands don't overstate their capabilities under load like the cheap no name units. You should be able to get by with about 400 watts and 18 or more amps on the 12v rail; corsair has the most rated amps on a single 12v rail, at 28 or more; some models have 66.