Contribution d'origine par : Philip Le Riche ,
Could be almost anything, but for starters, check you've reassembed it correctly, and in particular, all ribbons are fully home and locked in their sockets. Also, check carefully for any signs of water damage or resulting corrosion. These may be fatal, but try cleaning up any corrosion or contamination with isopropyl alcohol before giving up. If you can't fix it, look out for another of the same model on eBay advertised as "spares or repair" and try swapping parts. You might become an expert on that model and end up fixing and reselling a few, though you're not going to get rich!