Cat5 Wiring Problem

I recently wired my house in North Florida with riser-rated cat5 cabling. The cable was pulled through the walls, across the attic, to an 8-port switch in an unfinished bonus room above my garage.

Everything works fine during the warm months, but when the overnight temperature drops near freezing, everything seems to stop working (yes, it does get a little cold in North Florida). Basically, it works during the day, but stops working at night. The switch is your typical home networking type (i.e. cheap), but I’ve also tried it with an old 24-port HP AdvanceStack 10base-T hub I had laying around at the office, but the problem persists.

Any ideas?