mystery laptop

[Lethalpcnerd]

see im repairing a hey day acer travelmate 4062 lci,..when i switch it on it boots fine and all is responding until the logon screen where the mouse and keyboard stops responding hence cant login..i cannot say its hanging coz the typing cursor keeps on flicking..,power button also stops responding,so a battery pull switchz it off...it works fine in safe mode...tryd changing os bt same thing...what could be the cause??