MacBook only writes uppercase

Good morning all.

I'm writing to try to find a solution to a problem I'm having with my MacBook. For the past week the MacBook has only been able to type uppercase letters and hence the symbols associated to the number keys. After troubleshooting for a while I have reached the conclusion that it is not an issue of the keyboard:

- Caps lock is not stuck (light indicator turns on and off when pushed).

-Shift keys are not stuck (if this was the case typing with caps lock on would revert the upper case into lower case and this is not the case).

This issue is causing the MacBook to always startup in safe mode, since pressing shift while starting up will launch safe mode. After the troubleshooting I and investigating the problem online (reading other posts of people with the same problem), I believe that it is an issue with the PRAM. It is mentioned online that to reset PRAM you must press 'option, command, p and r' to reset PRAM, but it is not working for me. I imagine that it is due to the fact that the cumputer thinks I'm pressing 'shift, option, command, p and r'.

I have tried using an external keyboard and this works fine, typing lower case and upper case. Still I cannot use this keyboard to reset PRAM since I assume that the MacBook does not recognise any USB devices until it has launched the OS.

Any help on the matter or on how to reset the PRAM using any other procedure will be greatly appreciated.

Thanks,

CaraAnchoa