newly upgraded pc has no power

i recentlyupgraded my old computer's mobo, RAM, GPU and processor. the problem is, when i tried to boot it the comp is not reacting. there is no power. what could be the problem?

check your PSU capacity atleast minimum 500 or 650watts kung i7 yan...

Check the compatibility and also upgrade your power supply.

the mobo is gigabyte ma790fxt-ud5p
cpu is amd phenom2 x4 2.6
ram is pqi pc3 10600
gpu is sapphire radeon hd 4850
power sup is the stock 300watt psu.

di ba kaya nung psu pag ganun kababa yung spec?

2plugs lang ang power diba? yung 4pin at 20pin? tapos yung ibang power socket goes sa cd, hdd at fdd? lahat ba ng cable sa case kelangan nakakabit sa mobo?

im able to fix the prob. turns out the +/- mark on the power switch cable is incorrect. thanks for the help guys.

strange fans are running pero no beep and no display. tapos parang hindi tuloy tuloy yung ikot ng gpu fan. parang may rhytm. 1 short and 1 long. psu ba prob nun?

i guess psu nga problem mo, 300 watts lang kasi, upgrade mo na ng 500 watts or higher,

sobrang overload yang 300 watts bro. You should change that too. 500 sa generic, or 450 sa branded. You may experience little incovenience now, sooner of later uusok nalang yan. Naexperience ko na yan.

i'll try to look for a psu tomorrow. anyways ito pa naobserve ko, pag nakatayo yung cpu ayaw mag on. pero pag nakahiga nag oon siya. pero nag bblink yung ilaw ng gpu tapos yun nga yung fan parang 1 short 1 long interval. tapos walang beep. tama kaya yung pag kaka connect k ng hardware?
senxa na kng pinapahaba ko hehehe just making sure na magawa ko lahat to bukas. hehehe been working for it for 2 days na. anyway thanks for the inputs.

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ok. replaced psu with a 550 watt psu. kaso ganun pa rin. nag oon pero walang beep sound. di ko rin maoff via power button. tinanggal ko na lahat ng mem at gpu pero wala beep

check mo yung connector from case switches to board baka may nakalimutan ka. check mo din ung board mo baka kailangan secondary 8pin power supply cable aside from main cable supply. kalimitan nasa taas ng processor yan naka locate. cheers!

nakabit ko yung 2 power cable (24 pin at 8 pin)
tapos power for hdd at cd
yung board may sarili siyang power botton kaya for the mean time di ko muna kinabit yung switches. speaker lang kinabit ko. pero ganun pa rin result. fan lang ang umiikot.