Sony Vaio FW56E - Help please!

I have a Sony FW56E which I am attempting to repair for a friend of mine. He previously sent it to a laptop repair centre after slight water damage and was told the motherboard needed replacing. They wanted an extortionate amount of money and so I volunteered to do the repair. Motherboard has been replaced and also found the inverter was blown so have also replaced but still have no output to the screen or external monitor. Power light comes on, HDD comes on, processor fan runs at intervals as it should but just nothing to the screen. Also not getting any sort of post beeps. Have tried unseating the RAM and also tried the powering on with the battery removed and power cable in but still no joy. The keyboard shows some signs of residue on the back so i would imagine will need replacing but I can't imagine this beinthe problem. I have rebuilt and replaced parts on a few laptops before and don’t mind admitting being a little bemused by this one!! Any ideas or help would be greatly appreciated. Thanks in advance!