Latency issues when listening back

I'm at my wits end here guys. I recently upgraded my PC to a much faster model and re installed pro tools LE 8 on it (using Mbox 2). The problem is that when I record a vocal track and listen back, the vocal is lagging behind the instrumental. I've never had this problem before on my older less superior model. It's strange that I'm experiencing it now. Please help a guy out! =(