yeah, i'd start with clearing the browser cookies and then a restart. depends on what OS you are using as to how fast things are getting screwed up. when i was running win98se, i'd have to reboot at least once every 24 hours or i'd have mega problems. when i was running XP i think i rebooted 4 or 5 times in about 2 weeks.
also, since you've got a lot of people using the computer, if every time they are surfing the web and a pop-up box comes up to download "xxxxxxxxxx flash player" or "xxxxxxxx plug in" or whatnot, and they are downloading all of them....oh boy. when an excess of that has been happening, i used to just format out the hard drive and start fresh. was easier than going in and fixing things manually.