Task manager frozen

On my Inspiron 1720 running under Windows XP SP3, after having stopped a Chrome not responding, the complete task bar of Task manager is disappeared and if invoked Possible only after rebooting) it appears only a square without any other label and taskbar and is not possible to make it (the task manager) disappear unless switching off and on the computer. Running tasks appear correctly but it is not possible to act anymore on them. Can anybody help me to recover to the nornal operating condition of task manager?

Thanks in advance

Giampaolo