On Call Delivering excellent tech support can sometimes require heavy lifting, a feat The Register celebrates each Friday with a new instalment of On Call – the reader-contributed column that shares your stories of hoisting glitchy tech back to full function. This week, meet a reader we'll Regomize as "Harold" who told us he once worked as the IT Support Manager for a K-12 school. "We had just put in new Wi-Fi infrastructure to support every student from year 5 to 12 using a laptop," he explained to On Call. (The range covers fourth graders in elementary school all the way up to high school kids.) "It worked well for the first couple of weeks of term, but then we started getting reports that some of the laptops were intermittently unable to connect, or getting very slow connectivity in one area of the school," he told On Call. A little investigation revealed that only Windows laptops experienced the problem.…