This is a post for all the people that come here looking for help. Sometimes people don't post everything we'd need, and a lot of information keeps on getting reposted (an annoyance to everyone I'm sure.) So, I'm creating this post for people to be sent to so they have a starting place.

1st: Gathering information.
We need as much information as possible. If you don't know what you have try looking up documentation with the manufacturer (IE Apple, Dell, Gateway, Compaq, etc). They will generally have a support page for your model (look on the case for model numbers). It should list, what processor, socket, motherboard (maybe, sometimes just a model number), amount of basic memory it came with and/or the maximum it supports and the standards used.
If your having an issue with memory, make sure that its compatible with your motherboard (check at www.crucial.com). If your having trouble figuring out what socket your motherboard is or what processor you're using download the CPU-Z utility. It's a great program that can tell you what processor your using, what speed it runs at, what it's core voltage is. It can also tell you what motherboard you're using, and what memory as well. It can be downloaded at http://www.cpuid.com/cpuz.php Afterwards...

2nd: Determining the problem
Is the screen black when you turn it on? Does it turn on? Do you get any funny messages? What lights flicker? Is the internal speaker beeping? If so how many times? Try and note as much as possible and give as much description as you can.

3rd: Posting for help
Try and make your Title something relevant and descriptive. It will attract attention from people who have a good knowledge of the architecture. If you have a compaq with motherboard problems, IE Compaq [Model Number] Motherboard Issue. Someone who knows compaqs really well can zero in and help you. There are all kinds of quirky errors with different manufacturer's, but I doubt every person with that sort of knowledge has the time to sort through every "motherboard problem" post. After the title, the next step is the actual post which is the most important part. You want to start off with a description of the hardware,

Compaq Model "ABC123"
Pentium 4 Socket F
Motherboard MZ-123
Installed Memory:256 MB DDR PC3200 (2 DIMMS)
Maximum:1 GB PC3200

then post your error like so,

"Hi all, I'm having a problem. When I boot up, the BIOS screen shows I only have 128MB installed. I noticed 3 beeps when I start it up and a funny smell coming from the computer. Any idea what's
going on?"

Correct grammar, punctuation, and a friendly attitude are appreciated. No one here is getting paid to help you with your problem, so appreciate them with reputation if you found them helpful.

4th: Getting help
Generally someone, if not the forum mod themselves will post with their thoughts on what the error could be. They will suggest steps in which to get help, which you should follow closely. Don't forget to thank them.

5th: Replying with results
Reply what happened after you tried what the poster said. Whether it fixed it or it did something else (in which case go to step 2 and reply with a new description).

If your familiar and just looking for utilities, I suggest...

Ultimate Boot CD
http://www.ultimatebootcd.com/

Drive Fitness Test
http://www.hitachigst.com/hdd/support/download.htm
(Scroll down to Drive Fitness Test)

More to come...

For anyone who has had trouble with terms in this guide, I suggest taking a short read and going here
and here

Anyone who has something to add, PM me with the thing you want edited or just reply yourself

PS (Sticky appreciated.)