i find its more often bad contacts. no reason not to check fuses first. this happens a lot on later models when the screen ribbon is loose or dirty. it is very common for gba-sp to have a dirty screen ribbon or port. electrosolve contact cleaner works for me most of the time. the almost equal culprit is the power switch itself. the copper contact requires cleaning. electrosolve usually does the trick but realistically or just as often removing the shielding and wiping (careful not to bend) the copper contacts with eraser is required. (or replacement.)