"The mystery of the missing input signal" or "What on earth died in my computer?"

[Damazzian]

I recently moved to a new apartment, and while the computer worked fine prior that, it worked less than fine when I tried to start it afterwards - this in spite of the fact that we took great care in securing so that it would only be able to move a few centimeters horizontally during transport. Moreover, it had been sitting in a corner of the apartment for more than 24 hours before I got around to hooking it up.


The specs:
MB: Abit KN8 SLI /w nForce chipset
CPU: AMD Athlon +4400 64bit
PSU: Generic 400W
GPU: Asus Geforce 7900GS
RAM: 4 Kingston HyperX modules - 2x 512Mb, 2x 1Gb
HDDs: 2 Seagate Barracuda - 1x 60Gb, 1x 320Gb

Anyway, the problem is that the monitor gets no input signal. A small box displayed on the screen itself indicates that the monitor searches for analog or digital input - in vain. A few seconds later it slips into standby mode.
What I've done:

• Checked all cable connections, both external and internal, quite a few times. Had my brother over to double check it as well. No change.
• Checked monitor. I connected the monitor to my laptop, and was able to successfully display images from my laptop on the monitor.
• Checked that all the hardware is powered - all fans are running at normal speed and LEDs on the motherboard are lit up. Disconnected motherboard and graphics card power cables and then reconnected them. No change.
• Checked graphics card - removed it, inspected it looking for visually obvious damages, then put it back in. No change.
• Removed all four memory modules one by one - left in one module that is only a few months old. No change.
• Checked the appearance of the motherboard itself. I can spot no transistors or capacitors etc. that appear to be broken or otherwise damaged.
• Disconnected all drives - harddisk drives and an optical drive. No change.
• Connected a PC speaker I had stashed away. No POST beep is heard at start up. Removed the remaining memory module and started the computer. This triggered 1½-2 seconds beeps until I powered the computer off again.

Any suggestions as to how I proceed from here?

[Big_Daddy]

It could be a dead memory module. Keep swapping them in and out and see if it boots.

[Damazzian]

I feel relieved, embarrassed and puzzled at the same time. I inserted one memory module - lo and behold! I was rewarded with a boot splash screen!
This was accompanied by two beeps - a very short one, and a slightly longer one.

Then I inserted another module, wanting to find the faulty one... except I didn't. Now the boot splash screen appears, even with all four modules back in their place. I did clean the CPU fan a little bit, but not much, and I've seen fans way more dirty than this one in working computers. And now, the speaker beeps once when the computer is started, as it ought to.

I wish I knew what went wrong though - inserting the memory modules incorrectly seems to have been the issue here, but even if they became ever so slightly dislodged during transport, I put them back in several times since then and so I should have failed to insert at least one module properly each time for that to be plausible. And even then I believe it would have been visually evident to me that a module was not seated properly in its slot...so I suspect I was able to use the slot locks even though one or more modules wasn't seated right by a tiny margin.

Anyway, it's sorted for now. Thank you for pointing me in the right direction!

[UPDATE]
Windows ran, but was seemingly much more unstable than usual, and I soon fell into a restart loop. I was able to halt the loop and have Windows stop at a dreaded BSOD. I reinstalled, but to no avail. But seeing as my Kubuntu Linux ran as stable as ever, I began to suspect the aging 60Gb IDE drive Windows was installed on - and so I resolved to install Windows onto the same disk as Kubuntu. No problems whatsoever, and it has been running fine for the past 3 weeks or so. As the MBR was also installed onto this drive, I rather suspect that my initial problems were related to this drive, which I now believe to be ripe for replacement.