What is solution for computer restart again and again

Hi everyone.
when pressing the power switch, my computer successfuly opens, fans works fine, i cleaned the interior parts filled with dust but no usual beep sound heard in startup, no display than after a few sec, (maybe like 5-10sec) computer closes than opens again, its in cycle..unless i remove the power cord..maybe a problem in my cmos battery, processor, videocard or psu? I dont want to assume so i can make a sure decision for my computer. Im a college student and have less knowledge with computers. I hppe you fill me with knowledge. Thank you.