After starting computer an alarm starts and computer will not boot up.

What is the alarm that starts ?
Is it beep/s ?

Sounds like overheating

had a machine that made a beeping/siren type noise once, it was warning me that its temps were too high

There is a pause between beeps

okay thats a POST error code

the pitch/number/duration/frequency of beeps will tell you something, depending on what make your motherboard is.

okay thats a POST error code

the pitch/number/duration/frequency of beeps will tell you something, depending on what make your motherboard is.

Yup. The motherboard is trying to tell you that something is wrong. You need to find your mobo manual or look it up on the web to determine the error beep you are getting.

Quick and dirty - reseat all your mobo components and try to POST again. RAM, CPU, cables, etc.