1998 Vauxhall Vectra dash lights come on and off driving along and car whinges

Ok so a month ago i was driving along and my battery light comes on and the engine starts making this whinging noise when the revs get higher and the lights and internal lights would get brighter the more the revs went up. Took it to the garage and the bloke said the alternator was the problem so he changed it. Well last night im driving home and most of the dashboard lights start flashing on and off which is totally weird and as the revs go up the lights get brighter i tried driving it today and driving along the engine was getting really loud with the whinging. Im being told by a friend it could be the fanbelt but im unsure please help.