Hi,
Can you describe the noise a little better, is it beeps? If so how many (three short one long etc)?
What is the sound if it is not beeps?
Can you determine where it is coming from, your speakers or a part in your PC?
Your wattage is written on a plate on the power supply where you plug your mains power into the PC, it will be 250W 300W....
Do you know how much RAM you have in your PC? If you do not know what RAM is, go here:-
http://www.ncsu.edu/antivirus/troubleshooting/ram.php
Do you have a video card?
If so what is it?
Are all your fans working, power supply, CPU, case, video card?
Is the inside of your PC full of dust? If so, use compressed air if you can and a new paint brush and give it all a good clean.
If you do not know about something I have asked, just go to google and search for information about it on the net.