I've been putting together a new computer for my dad. I've learned a few lessons that may be helpful to other amateur system builders. Here are the important specs:

• Athlon XP 3000+
• ASUS A7N8X-VM/400 (nVidia chipset with graphics, audio, and network onboard)
• 512 MB PC-3200 RAM
• Western Digital 80 GB hard drive
• Benq DVD+RW
• 300W power supply

Once I assembled this system, it powered up, but it failed to display anything on the monitor. I did a little research and learned that the motherboard wants PC-2100 or PC-2700 RAM, not PC-3200, so we bought a stick of PC-2700 at a nearby shop. It made no difference. Then I put my trusty old Athlon Thunderbird in the CPU socket and the computer finally came to life. Lesson #1: the latest processors have a high failure rate; ask your vendor to test the CPU before shipping it.

The vendor replaced the CPU, thankfully. In the meantime, I discovered that AMD has a lot of online documentation (and videos) describing how to install a heat sink. This thumbnail-size chip pulls in 75 watts continuously, so if the heat sink doesn't make good contact, the chip can burn out in seconds. AMD recommends a thermal pad for "lidless" processors like Athlon XPs. I don't think I burned the original CPU, but I can't rule out the possibility. Lesson #2: installing the heat sink correctly is harder than you might think.

I started loading software, but the system was a bit unstable. It rebooted occasionally with no warning. After struggling for a while, I popped in the Gentoo install CD and typed "memtest". This memory test is far more thorough than the BIOS test and it revealed that the RAM was unstable. I put the PC 3200 stick back in and the machine finally worked perfectly. Lesson #3: thoroughly test your RAM before using the machine.

The machine worked well for a day, then suddenly switched off and wouldn't turn on again. The power supply failed. I didn't hear anything explode, but there was a faint burning smell. I swapped in a different 300W power supply to be sure that only the power supply had died. Whew, only $10 gone.

I've seen warnings about generic, low-end power supplies, but I felt like I had little reason for concern. When I plugged the computer into a watt meter, it showed that the whole computer consumed 130W when idle and 160W under load. There is a truth in advertising issue here, since a power supply rated for 300W should not fail under 53% load. After some research, I ordered a Thermaltake 420W unit. As a bonus, this power supply should provide extra airflow to cool the processor. Lesson #4: you apparently need a power supply rated for more than twice the maximum power your computer will consume. Also, name brands cost five times the price of generics, but it's worth the price.