The motherboard doesn’t fit in the case: this is simply a problem of ordering a motherboard without knowing the mobu type the case could hold. When you buy your computer case you need to be sure it can fit your motherboard. There are four types of motherboards; mini ITX, micro ATX, ATX and extended ATX. The way I have them listed here is from smallest to largest.
Using the wrong type of RAM; the newer RAM is often not compatible with older types of RAM, even if the slots are the same on the motherboard. DDR2 needs to be installed in a DDR2 specific motherboard. DDR3 is specific to DDR3 motherboards, etc.
RAM not operating at specified speed. If your DDR3 RAM is running at 1333 instead of the 1600MHz it was rated to operate, you will need to make some simple changes in the BIOS. Upping the multiplier in order to land at your rated speed is easy. But DDR3 RAM will default to 1333 unless it is a slower RAM speed. The newer RAM is not an install it and forget it RAM type. You may need to tweak it in BIOS to get it working properly and at full performance.
My computer keeps shutting itself off. This could be caused by your CPU overheating. If you did not install your thermal paste correctly overheating could occur. Remove the CPU cooler, scrape off the paste and install a thin layer (thick enough so that you cannot see the lettering on top of the CPU) and reinstall the cooler. Make sure there are no dirt particles or anything that could keep the cooler from sitting flat on top of the CPU heat spreader. It is also possible that your CPU cooler is not up to the task of keeping your CPU cool. If this is the case install a high quality aftermarket CPU cooler to lower the temps.
I can’t install the operating system; you will need to have a valid operating system key in order to install. The newer operating systems can only be installed on one PC at a time. The days of installing one copy of Windows onto several PC’s are gone. Now you need an individual key for each computer that you are running. Windows 7 will usually allow you to use the OS for 30 days without having a new key. Then it will shut itself down.
These are some common problems with new computer builds. Obviously, there are other issues too so you may experience a problem not mentioned here.
I have found building a computer to be a very easy and rewarding project. None of the above problems were enough to keep the computer from being built. You just make adjustments and keep going. Try your own computer building project; PC building is really not difficult and even my 12 year old daughter has done it.