From 300w psu i change it to 450w will that be ok?

it really took me a long time to solve my problem bout my computer, and here it is i found a nice site to share my problem hope you guys can help me solve my problem.

im always experiencing a problem regarding with my power supply everytime i purchase a new power supply it will work only less than 6 months. one of my friend suggested me that i will replace may atx 300w power supply to atx 450w and she explained me the reason why i should replace it,so i think she got a point and the other reason is atx 300w power supply is almost face out, so i follow her advice and buy a atx 450w power supply.when i tried to turn on my computer using a atx 450w power supply it does not work but the LED in the motherboard lights, but the fan from the process is not working, no beep sounds from the board, i try many times to check all the connections and i think i connect them in proper. i have a p4s133 asus motherboard. Is anyone familiars the connections of a p4s133 asus motherboard? because im a little bit confuse with the connection beside the motherboard supply the AUX ports i think, should i put a supply on that? what should i check first to solve my problem? and replacing a atx 300w power supply to 450w power supply will that be ok? should i separate the power outlet of my monitor? because my monitor is connecting to my cpu.

your reply is really a big help for to solve my problem... thank you!!!

ivy