Sometimes after a software (system) or hardware upgrade even Macs can have some problems; if you have tried every solution without success you could try this.
Every Mac stores certain settings in a special memory area even if it is turned off. On Intel-based Macs, this is stored in memory known as NVRAM; on PowerPC-based Macs, this is stored in memory known as PRAM.
Another step to try is Resetting the System Management Controller (SMC). An SMC reset should only be attempted after all other standard troubleshooting has been performed.