We've been getting a few very strange problems here at I&TS, all derived from a common cause. The issue often seems to be that people do not restart or shut down their computers for long periods of time.
While I&TS requests people leave their computers on Thursday nights for upgrades, some people never shut down their computers. This isn't bad in the short term, but if left on for weeks on end, there are sometimes issues with connecting with the network. You may not be able to find files you want, or have a slow login time as files are synchronized.
It also uses extra energy, of course. Most computers go into sleep mode, so only use a little power, but it's more than if the computer is turned off.
It's good practice to turn off the computer every once in awhile. For instance, on Friday you can shut it down for the weekend.
Also, if you suddenly can't find files (and you know you haven't deleted them), try restarting the computer and synchronizing. It may fix things.