All things must pass. My old Dell computer has served me well in my office for a half-dozen years or so, plugging away long before I got my little Gateway Tablet. But when a recycling offer came along, I realized it was time to let the old machine go. After all, I had two other computers I could use in the office, and each one takes up space, so I had it toted off to be piled in with the other machines on campus.
Several students in past years have written about computer recycling, and I've read some on my own, and the news isn't always good; although some companies do offer programs to extract key polluting elements from cast-off electronics, some just get the offending electronics out of the country. Check the EPA for a list of contacts for electronics recycling.