Computer beeping every hour among other issues

[Red_Apple27]

Windows 7 Home Premium HP w1858
Manufacturer: Hawlett-Packard Company
Model: s5213w
Processor: AMD Sempron (tm) Processor LE-1250 2.20GHz
Installed memory (RAM): 4.00 GB
System Type: 64-bit Operating System
Graphics Card: ATI Radeon HD 5450

My issue didn't start till about 4 months ago. Whenever playing an online game such as Team Fortress 2 it would slow down (lag) or be choppy at times. Wouldn't happen everyday, till about a month ago, when the beeping started. It happens every hour, it is a weak beep but it comes from the inside of my computer. Also, I can't run Team Fortress 2 without it crashing every 5-10 minutes of playing. I have also noticed my whole computer has become a lot slower. I'd like to know if this can be fixed or if I should just get rid of this computer and get a new one. I would really appreciate the help.

Thanks in advance.

 

[scout_03]

i little dust off and when was the last time you defrag the hdd and clean all the old cookies an other you dont use ?