PC tripping breaker

I have an E Machine T5020 and have had it for about a year and a half now.Up until about 4 days ago I had'nt had a single problem or complaint,thats when the circuit breaker that controls the power outlets in my desk area started tripping.I can log on and usually work for about 3 or 4 hours and then POOF!I havent added anything new to my PC nor have I added anything new to the circuit that may be interfering.I took turns unplugging different items that are opperating on the same circuit such as my printer,monitor,speakers,etc.it kept tripping until I unplugged my main power cord to my tower.Is it possible that it may be something as simple as a collection of dust inside the cabinet thus causing a tempurature increase, but then wouldnt there be like a thermal overload device that would just shut down the system and not cause the whole supply circuit to become cold ? I'm just hoping that it something simple and inexpensive that possibly I could correct on my own.Any ideas folks? Thanks in advance for your help !