The t.v. may have been dropped or shaken a bit. This is a very common problem with tv's and sometimes the colors has just lost their alignment. Some easy ways to fix this problem is to perform a color convergence on the t.v.
Either something hit your screen or it is just super old. Either way it is time to get a replacement. You might be able to have a repairman fix it if a new tv is not an option.
