cd-rom reading error

the cd-rom drive asus 50x max is running in Pentiun-III 450Mhz under windows xp pro. the drive is detected but when you insert a cd and try to read it, an error message pops out saying ‘please insert cd’ or ‘not ready reading drive f’. another problem of this cd-rom drive is sometimes the cd tray opens sometimes it does not. what do you think is the problem of this drive? is it the power supply of the power connector or the ide cable or something else? please give me a help.