A typical 60 lb. desktop computer contains the following materials that can become waste:
 

Material

% of Weight Weight (lbs.) Current Recycling Efficiency Use / Location

Plastics

23% 13.8 20% cabling and housing
Iron 20% 12.3 80%  structural, magnetivity/(steel) housing
Aluminum 14% 8.5 80% structural, conductivity/housing
Copper 7% 4.2 90% conductivity/connectors
Lead 6% 3.8 5% metal joining, radiation shield
Zinc 2% 1.3 60% battery, phosphor emitter
Tin 1% 0.6 70% metal joining
Nickel 1% 0.5 80% structural, magnetivity/(steel) housing
Cadmium <1% 0.1 0% battery, glu-green phosphor emitter/housing
Manganese <1% <0.1 0% battery, glu-green phosphor emitter/housing
Cobalt <1% <0.1 85% structural, magnetivity/(steel) housing
Selenium <1% <0.1 70% rectifiers, PWB, connectors
Mercury <1% <0.1 0% batteries, switches/housing
Arsenic <1% <0.1 0% doping agents in transistors
Gold <1% <0.1 99% connectivity, conductivity/PWB, connectors
Silver <1% <0.1 98% conductivitty/PWB, connectors

Adapted from SVTC's Compositon of a Personal Desktop Computer