A Playstation 2 controller may stop responding or functioning due to a break in connectivity, the presence of static electricity, improper software formatting or hardware damage. Outright damage to the piece itself can be caused by exposure to temperatures or levels of moisture that are detrimental to Playstation 2 controllers.
In assessing a Playstation 2 controller's functionality, first check the actual connection. Operating via a wired line, this is potentially compromised if not secure at either end or if frayed or damaged along the line. Substitute a working controller if possible to check the machine's reception to functioning controllers. Next, examine the piece itself, taking age and exposure into account.