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.