Hey i was wondering what the problem can be with my amp... I have had this Marshall amp for about 3 years but only tonight has it started acting weird...When playing the sound is pefectly fine but once and awhile it will fade in and out... can anyone help?

First I would check the basics like your cable or plug your guitar into another amp and see if the same thing happens.

Do you hear any pops,scratchy sounds?

yeah check all the basics first like Brian said.