Acer Aspire 5920 keyboard problem

Hi I'm new to posting here, here goes I have an Acer Aspire 5920 with a very strange keyboard problem, some keys type different symbols others dont work at all and others work fine, This the second replacement keyboard I've tested on this laptop (used but both from a 5920 laptop) and the problem still seems to be there, strange but a usb keyboard works fine, I was considering buying a new Keyboard for this but now i'm not sure if its even a keyboard issue, forgot to mention the think the guy said the powerboard has been replaced on it, this is not my laptop but I think the keyboard worked fine before this, any help appreciated on this difficult one  

Thanks for your reply qhn, wow your some poster here 53,000 posts  well I had a look at the other posts and did manage to unplug the CMOS battery cable but still the problem exists and can't flash the BIOS with latest 3813 for some reason, I also changed HDD  reseated the Ram modules but still no use 

Finally decided to send Laptop to a service dept for repair (non Acer) will let you know in a few days how I got on, oh and tks for the help qhn  keep on posting

This Laptop problem has been a difficult one, service people kept it for 2 weeks trying to locate and fix the problem (so they told me anyway), well the good news is that they fixed it but as to how I'm not all that sure, all I know is they eventually replaced the keyboard with one that worked but I'm told earlier keyboards didn't work, so there you have it Laptop will be back with its owner tomorrow and I hope they will be happy with the result, I for one am happy that it worked out well in the end, thanks for the advice guys I appreciate it, until next time take care (wont be very long I'm sure)