Dell having trouble with booting up making the siren noise

[balla]

Hi all i have a dell sc420 and my specs are pentium 4 2.8 ht and 512mb ram. The problem is that when i boot up the computer it makes a loud siren noise maybe about 4-5 times.Also during that time the cooling fan gets a lot louder for some reason. I dont know if it is the power supply or cooling fan. The monitor screen stays black and doesnt work. Any help would be nice thank you.

 

[kirock]

Well siren noises aren't my specialty but I'll give it a shot.
Can you smell anything burning?
Do you hear/see the fans turn on? If it doesn't POST, ie. screen blank, it's either dead CPU or dead 5Volt output on the power supply (assuming the graphics card and display is/was working).
Is the siren sound coming from the speakers or some part of the PC?
Do you hear any beeps during/before/after the siren noise?

 

[balla]

well its coming internally from the pc and actually it beeps 6 times in a high pitched annoyin noise. I actually think its the cooling fan and its not the cpu thats dead bc its basically brand new. Also previous times i would have to turn off and on the computer several times for it to work. I have come to the conclusion that it is the cpu because the power supply fan is not working.