ibook g4 weird power button problem

so i replaced my hard drive in my 2005 1.33ghz ibook g4 from a 40gb hard drive to 160gb. before i did this everything was working fine. after the install my ibook started acting really weird. when you press the power button there is no dong and nothing happens. after leaving the ibook plugged in for a couple hours however it finally works and can turn on. the ibook charges and the battery works great. i can even put it in sleep mode and i have no trouble waking it up. the problem comes when i shut the ibook down if i want to immediately turn it on the power button does not work and i have to wait a couple hours to turn it on. ive already tried doing a pmu reset and a nvram reset. it doesn't seem to work. i also used to be able to push the power button to bring up the shutdown menu and now that doesn't work either. i guess for now il leave it in sleepmode all the time. but how should i go about fixing this. i want to sell this computer soon so i can get some money for a new laptop for school.