Given so little information, I can only guess the machine needs service or repair. It's not unusual that a machine after many years will havd dust bunnies inside clogging airflow causing an overheating condition and the result being something like you wrote.
Bob
Hi there, The problem is with my 4 year old packard bell 17" monitor. Sometimes when i am playing runescape the monitor will just get a multicoloured line accross it and freeze, and other times when i load up msn messenger after playing runescape my pc freezes.
Any ideas?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic