After a lot of people have posted with issues, I figured - this might help. It was originally a reply to a post, but I'm putting it here so that people will hopefully see it and get some benefit. This covers the most basic setup of the computer, which will enable smooth running and future good use.

First off, contrary to what many will advise, I can safely say that on a well optimised, fully up-to-date system, UAC can be left enabled without harm (And that's on a 64-bit, Windows 7 machine with 8GB of memory; traditionally the sort of system that caused issues with this service). Also, disabling UAC opens an unacceptable level of system penetration posibilities. If you look into the security hazards, it's far better to leave on. Sort of like a firewall - you don't turn that off, because without it your system has more penetration holes than a cheesegrater.

My advice to people who are having issues is to concentrate on checking all your drivers. People traditionally don't look at things like the motherboard chipset, SATA and networking drivers, because they're not 'sexy' and advertised like the GPU driver, however without them a system will have many issues - especially the chipset drivers. For instance, a system that I built was having rebooting and blue-screen issues. I didn't realise that the user had re-installed the OS (Turns out they wanted a different version than I'd installed, natch) and when troubleshooting I'd discounted the drivers. Anyway, when I did finally do a full check, it was still using the OS default drivers. A quick update, and all the bluescreens, freezes, lockups and crashes went away.

You want to ensure that:

• AHCI is enabled in the BIOS BEFORE you install the OS.
• The latest chipset drivers are installed.
• The latest SATA drivers are installed.
• The latest network drivers are installed.
  
  • Note: These may all come as one pack from your motherboard manufacturer, it's worth checking. However, it's often more likely that you'll be able to get newer versions by downloading them individually.
• The latest sound drivers are installed.
• The latest GPU drivers are installed.
• Any peripherals (Xbox 360 pad, mouse, steering wheel, etc.) all have the latest drivers.
• You've got the latest versions of the .NET Framework (Should come through windows update).
• You've got the latest PhysX drivers.
• You've got the latest C++ Runtimes (Both 2005 and 2008).
• You're running a solid, compatible antivirus that doesn't attempt to control your machine (Good examples of free AV: Microsoft Security Essentials, Avast! Home).
• UAC (Windows 7 only) is still enabled.
• Windows Firewall (Windows 7 only) is still enabled.

Now that you've got all these various aspects covered, your system should be running with minimal issues, and be relatively maintenance free (Assuming you're not installing every piece of crap that tries to download itself from Facebook or Myspace or other such dodgy sites).

Regarding the AHCI point - if this has not been enabled on an already existing system, DO NOT ENABLE IT. You may potentially prevent the system from booting into the existing OS. Only enable this prior to a complete wipe and re-install of the OS. If you are sensible and have the OS on one drive, and the data and other such on another drive, you will be able to continue with just a re-install of the OS and essential applications - a minimal impact.

Once you've done this, if you're still experiencing issues, feel free to look into more esoteric solutions - hardware failures (Particularly power supply related) are uncommon, but can slowly cause degredation in the performance of the system (Especially if, due to capacitor bleed, your PSU is just slowly reaching the limits of its capability to power your system).

Very nice post, thanks for this contribution LazerFX. I've now put this as a sticky on the forum.

Cool, thanks! I just hope it helps someone...

I've successfully installed AHCI AFTER installing Windows 7 - there is a registry update for this. However, I agree only do this if you confident and don't mind reinstalling if something doesn't go to plan

Technically, you've put Windows into a compatibility mode - you're not getting the full performance from the AHCI system... however, yes you can do it, it's just not good to do it

YOu need to have UAC on, this conflicts with other thing I use my computer for :/

If it's a legitimate issue (And, to be frank, I've not come across one that can't be worked around yet), then sure - disable UAC. However, I strongly don't reccomend doing it as you're losing another layer of 'armour' against unwanted program execution.

It's often better to run the specific application as an administrator, or in compatibility mode, or some of the other UAC workarounds than to drop the entire systems security for the sake of one application.

In the most extreme case, I'd much rather use a Virtual PC to run the application (If you've a high enough version of Windows 7, the in-built XP Mode) rather than drop UAC; but those are relatively complicated technical workarounds.

So much in the way of possible, and very inappropriate jokes could be made...
But I'll just say thanks, reading this made my day cause I'm childish.