iphone 3gs

[completely iris]

Ok so here's the problem, I replaced the lcd screen on the iphone 3gs and it was the wrong one so I had to reorder the correct screen and when it came I fitted it perfectly, because the phone hadn't been charged in 5 days I assumed it was completely drained and put in on charge with the wall charger, after 2 hours I checked it and it wouldn't turn on, I tried the holding power and home button for 20 seconds and it flashed up on screen with the battery sign and charging, I left it on charge for a further 4 hours and went back to it, again I had to hold the power and home button to get any sign of life and nothing had changed, I have charged it over night and when I tried turning it on thismorning, I am getting nothing at all. I tried holding power and home again and am getting nothing at all now... What do I do??? Worst thing is its not even my phone, its my 67 year old neighbours and I can't afford to replace it... In serious need of serious help... Pleeeeaaasssee