Macbook without start up sound

Question

Good morning everyone.
I´ll tell you a little about my problem. I have a macbook 13" mid 2010 mod A1342. Last week, after cleaning with a cleaning foam for PC´s, I think i used so much foam into the keyboard, because i started up and wont start, i let pass time and tried to start up, it started but some keys was in dead short, and the laptop turns off, i cleaned again with fairly isopropyl alcohol in the entire surface and the back of the keyboard, i wait for it to dry for 2 days and the in tried again, the mac start and works fine without pushing any key, but some key was making dead short, i was using my iphone as a wireless keyboard the trackpad works fine.
Consulting with an apple tech center they pdiagnosed the keyboard probably was in dead short and but i have to left them to a entire diagnose.
I buy the piece(upper case) and i replaced by my self (i´m a desktop support techinician for mac and windows), the macbook works fine again with all the keys including mutimedia keys. but the start up sound was gone, now the sound is very low, the speakers works fine i probe it whit de audio midi config. app, i disconnect the speaker off the board, the spearkers of the keyboard works fine but with a very low sound, when i put a headphone or an external speakers the soud works very fine and with a hig volume.
Due to the constant reebots without turn off properly, the volume(image) of the mac was corrupt, i´ve tried to repair it with the Disc Utility app but the volume was very damaged, i tried to reinstall preserving my files but there´s no oprtion for that , the only option was a clean installation. i think a clean installation fix the trouble, but the sound was the same, after installing all the updates to this day, the result was the same. In the information menu displays onboard sound, in the prefs pane the output have onboard sound to play sounds, i configured into the audio and midi app the stereo option, bunt the sound is still low.
I don´t think the problem was the logic, beacuse it plays sound into headphones and the internal speaker and the keybooard speaker, the problem is only the startup sound gone and the level of the sound is very low (sound like a cell phone). i tried to reset the PRAM, in the faqs apple say that i have to hear 2 startups sounds and the i have to realease the pushed keys, but in my case there´s no sound, the laptop restart as they say, but without sound, i´m not sure if the PRAM was restored or not, i push the keys (cmd+op+p+r) turn the MB it try to start the a little bit reboot by it self, tyr to start, again reboot by it self, but without sound, if i keep pushing the keys the procees won´t stop, if i release the keys the macbook start fine(without sound), but i not sure if the PRAM was restored.
I hope anyone can help me.

Answer 1

i also got this kind of problem recently. i was connected to a speaker n the start up sound just didnt come out till i plugged out the speaker jack. this happen after i finished reinstalling my mac os x (snow leopard) including the updates. the condition worsen by having a delay when i started up my mbp for the 3rd or 4th times. the screen just black n i got a delay for 3 to 4 seconds till finally i heard the start up sound back n see the apple logo n the loading gear came out. i later restarted the mbp again to see whether the same problem occurs bt somehow it didnt. weird things happen to my mbp these days.. what should i do? any suggestion? :O