I don't know whats wrong with my car ?

[FL Boxster]

i think its an electrical problem but anyway ....when i turn on the CD player or radio after a while the music starts to chop and i hear these posses in the radio/CD and if i hit the brakes the front lights dim a little the same thing happens when i press the windows buttons its getting worse with time. it used to do that once a week or so now its happening everyday.

Can anyone Help ?!

Thanks