1. A power-on method for a computer system comprising a processor supporting Hyper-Threading, a Read Only Memory (ROM) and a main memory, wherein the processor comprises a cache memory and the ROM comprises BIOS codes, the power-on method comprising: initializing the processor in a Hyper-Threading disabled mode; copying the BIOS codes from the ROM to the cache memory; initializing the main memory by executing the BIOS codes in the cache memory; and re-initializing the processor in a Hyper-Threading enabled mode after the main memory is initialized.