Case 1: My desktop PC at home. It is a home-brew AMD XP 6000 system. I admittedly went extremely cheap on the motherboard to try and save a few bucks. The motherboard is a Biostar NF-520-A2 that I bought from Newegg for 48.99. Running 2GB G-Skill RAM, and a Maxtor 320GB SATA HDD.
The symptoms: Computer was running just fine, until one day it began running very slowly and locking up every time my wife tried to load Firefox or any other application for that matter. The computer would boot fine, but couldn't load any applications without locking up. It wouldn't BSOD, the screen would just freeze, with the cursor locked in place. I put off fixing the machine for a few days, but I immediately suspected the RAM.
We have another AMD based machine upstairs, so when I began troubleshooting, I pulled the RAM from it to see if that would clear our problems up. I swapped the RAM, and attempted boot. I got an error that a system file was corrupt, and needed to be replaced. I attempted to go in through the recovery console using the Win XP boot disk. While booting, I got a blue screen of death. I boot again. Blue screen again. I booted one more time, and begin getting another error. I am getting a 'No OS found, please insert system disk'. This is not good.
I rebooted the machine, and went into the BIOS setup. Lo and behold, the BIOS was no longer recognizing the SATA drive. I check the connections to the SATA drive and they are all good. I go back into BIOS and hit "auto detect" a few times to see if BIOS will recognize the drive.
Now, of course, I am thinking the problem has been a failing HDD all along. On a whim, I decided to switch from SATA port 1 to SATA port 2 on the motherboard. The system boots right into Windows XP, and all appears to be fine. I run CHKDSK, and a few minor errors are reported and fixed. The system has run fine ever since. My final prognosis is a failed SATA port on the motherboard.
Case 2: Mother-in-law calls frantically. She operates a travel agency business from her home. All of her files are on her office computer. There has a been a power outage, preceded by what sounded like a power surge at her house. The plug-in desktop calculator on the same AC circuit as her computer is fried. Scary situation.
The machine is a 2.8GHz Celeron by Compaq. Since the power outage, whenever the computer is plugged in, the back of the power supply and the front panel power button both just flash green. When the power button is depressed, nothing happens. The lights just continue to flash green.
After talking to her for a few minutes, I realize there has been some power problem at the house. I reassure her that it is probably just the powersupply, and not to worry about the hard drive just yet. It turns out that there are quite a few important files on the computer. Has she done a backup recently? Of course not!
I google the flashing green light issue, and see quite a few "Replace power supply" remedies on Google. When I get the computer, I cannabilize the power supply from an old computer I have around the house for it's power supply.
After replacing the power supply, the machine boots up flawlessly. Another problem solved quickly.
In the first problem, I suspected the RAM was bad, and it turned out to be a failed SATA port. Second case, my first instinct was a bad powersupply, my Google search backed it up, and the problem did indeed end up being a power suppply. Sometimes troubleshooting is straightforward. Sometimes you just gotta screw around until you get things to work.
Switching SATA ports on the first computer was an educated guess however. When I booted the computer, I could hear the drive spin up normally, with no funky sounds. My instict was that the harddrive was good, so I started to suspect the motherboard. If switching SATA ports had failed the next step would be to try a known good HDD out, and see if BIOS recognized it.
Now I just have to figure out what to do with this Biostar board. Run with it on one SATA port, or RMA it? Knowing me, it's staying right where it is.