"No power but light at magsafe"に関する回答you MAY want to check SN of the mac just on the odd chance that its still under Warrenty ( highly doubtfull) . new systemboards are not cheap for macs but also not impossible to source a refurb ..
"How to clean LCD properly?"に関する回答Well since we cant get the OMNICLEANZ here anymore ... homebrew something almost as good as follows . You REALLY should avoid anything that contains the likes of ammonia, acetone, toluene or ethyl alcohol , as these are solvents and while great at disolving oil based fingerprints , they are also quite good at disolving oil based plastics and removing Uv and other coatings on your LCD/LED screen ( glass covered screens have less issues with your windex type stuff, But most of these things still leave a bit of residue behind , which will require buffing out anyway , and any oilphobic , uva , glareproofing ect coatings are at risk with chemical ,or physical friction, for this reason use minimal pressure while cleaning ) so, IMO better to have the safest option on hand to aviod potenial mistakes when in a jam) . I find the smaller atomizing bottles desgined for lens cleaner (like what you get for camera lens or eyeglasses) easy to carry in my geek bag , but DO rinse well prior to filling up with something...