Computer speed

My pc is running at a alarming speed my clock for example is running approx 4min faster than it should in opther words in 1 minutes time my pc clock does 4 minutes ive tried everything i can think of to solve the problem but to no avail can anyone give me some help or advice on what could be causing this.
i bought this pc second hand and have had the problem since then its a amd system with a 800Mhz CPU with 120 meg ram running win 98se
thankyou to anyone who answers