#5. IBM PS/1 (1990-1994)
Among other brilliant moves, the original PS/1 featured a power supply inside the monitor, which made swapping out displays impossible, and it couldn't accept standard ISA cards, preventing upgrades. (Later models were more compatible.)
In 1994 IBM abandoned the PS/1 and tried again to capture the consumer market by introducing the Aptiva line, but this too was largely a disaster. IBM gave up the whole Aptiva idea in 2000.