“Known-Working” Doesn’t Mean “New” To perform parts exchanges for troubleshooting, you need replacement parts. If you don’t have spare parts, it’s very tempting to go to the computer store and buy some new components. Instead, take a spare system that’s similar to the “sick” computer, make sure that it works, and then use it for parts. Why? Just because it’s new doesn’t mean it works. I once replaced the air conditioning compressor on my van with a brand-new, lifetime-warranty alternator that failed in less than a week, and six more replacements failed (all from the same batch or defective parts). Whether it’s a cable, a video card, a monitor, or some other component, try using a known-working item as a temporary replacement rather than brand-new. Rather than give away, sell, or discard working video cards, hard disks, and other components you have replaced with faster, bigger, better upgrades, keep at least one of each item to use as a replacement for testing purpo...