You can learn to assemble a PC on your own.
When building a rig, two things are absolutely important: the first is "budget"-- how much are you willing to spend; and the second is "purpose" -- what do you want and need to do on the computer that you're building.
As for choosing parts, it also boils down to those same two things. In other words,
1. What do you want/need to do with the computer?
2. How much can you spend for it?
You can either ask a friend to show you, or watch video tutorials online. Some motherboard manuals have instructions on installing components like the processor, heatsink, etc.
Make sure that the parts are compatible with each other: processor and motherboard must be of the same socket, RAM type must be correct, etc. Keep everything in their boxes and anti-static bags until you're ready to build.
Memory Modules
Which is a better option for choosing memories? "1pc of 8Gb" or "2pcs of 4Gb" or "4pcs of 2Gb" ?
Consider these points:
1. Motherboard compatibility (can it use the 8GB RAM module?)
2. price (is it more expensive than 2 x 4GB ?)
3. future upgrade plans (aiming for 16GB in a year or two?)
Consider this scenario as well:
If you have 1 x 8GB, and it fails in the future, your PC is unusable until the RAM is replaced; but if you have 2 x 4GB and one of them fails, you can remove it and still use your computer.
Video Cards
Choosing video cards is generally dependent on the games that you want to play, at what resolutions you want to play them, and at what detail level. Check the minimum and recommended system requirements of the games and compare with this video card hierarchy table courtesy of Tom's Hardware:
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html
Regarding power consumption, read the tables on the link below, especially the third one, where both processor and video card are stress-tested and the power consumption measured:
http://www.silentpcreview.com/article1245-page3.html
The article concludes that for many systems, having a PSU greater than 500w is only necessary when using ultra high-end video cards or setting up a multi-video card (CrossFireX or SLI) rig. Most systems will run fine on 400w or even 350w PSUs.
For watching 1080p movies, you can take advantage of the i5-3570's Quick Sync function to decode videos with minimum CPU consumption. For that you need a media player application that supports it. AFAIK Windows Media Player doesn't. You can use Potplayer http://www.digital-digest.com/software/PotPlayer.html or LAV Filter http://code.google.com/p/lavfilters/ + MPC-HC http://www.videohelp.com/tools/Media-Player-Classic-Home-Cinema
Then you can try frame interpolation with SVP http://www.svp-team.com/ to see if you like it or not.
SSDs or HDDs?
SSDs are Solid State Drives. Basically it's a very fast and sophisticated flash drive. It's primary advantage compared to hard drives is faster access time and higher transfer speeds. With SSDs, Windows 7 can start up within 1 minute (the fastest even less than 30 seconds), applications can launch almost instantly. Overall responsiveness increases.
However, like other flash devices, SSDs have a limit to the number of times it can be written to (10,000-100,000 writes per block). SSDs mitigate this by using methods like wear-leveling (spread erasures and rewrites across the disk so no block is written more often than others) and having extra blocks/sectors to replace those that have already failed.
While it can be convenient to use 1 large SSD to replace the HDD, high prices make this somewhat impractical. What some people do is get a small SSD (40-80GB) for the operating system and programs, and a normal HDD for file/document storage.
Windows 7 is recommended for SSD installs.
Computer Case, Casing or Enclosures
Case selection is very subjective. Most casings with standard sizes have decent airflow.
Monitors
Please also be reminded that in any PC Setup, the display is always the last piece of equipment that is the least upgraded/replaced. Sa katunayan, hanggat pwedeng gamitin, ginagamit unlike sa components inside the PC Casing. Kaya kailangan, sa unang bili pa lang ng display, future proof na kaagad.
Choose a monitor that has HDMI or DVI port connections. The reason I prefer HDMI and DVI is because they are digital connections from the computer to the LCD.
VGA is an analog connection, which was OK in the days of CRTs. The digital video signal is converted to analog in the video card, then sent to the monitor.
But LCDs are digital devices. So when they are connected via VGA, the analog VGA signal is converted back to digital inside the LCD. This analog-to-digital (A/D) conversion can result in video degradation like this:
The cause can be cheap VGA cables, poorly-implemented A/D converters inside the LCD, or both.
But when DVI or HDMI is used, the connection is digital all the way, and no signal degradation occurs as a result.
Unfortunately DVI and HDMI inputs usually found in 19 inch LCDs and larger.
PSUs
Change your mindset about getting cheap with PSUs. It's the most important yet taken for granted part of a computer system. Avoid generic PSUs like the plague. Getting a generic PSU is never a good idea. Convert from a generic PSU to a branded one to accommodate a better GPU to maintain the components of your computer in great condition. Generic PSUs omit many safety features just to keep costs low. Most don't have thermal sensors, inadequate surge and over-voltage protection. Don't skimp on the power supply, but don't overspend either.
Operating System
Make sure that you use a 64-bit operating system (OS) to make use of all that RAM. The reason I recommended using a 64-bit OS is that a 32-bit OS has a limit on the amount of RAM that it can use. Theoretically it's 4GB, but in practice, it's between 3 to 3.5 GB. You can run 32-bit Windows on a PC with 8GB, but you can only use 3-3.5GB of it, which makes the extra RAM useless.
