I assume you are talking about drop outs?
Usually it's caused by a peak of load that your system can't carry.
As Ken above suggests, the basic info is needed in order to guess anything. What do your projects include and what kind of a PC do you have? How are your buffer settings?
Are your drivers Tascams own ASIO or ASIO4ALL (which is a WDM wrapper)
One very common cause of drop outs is that one tries to record with very resource heavy mastering plugins inserted.
You've been a member for two years with nearly 300 posts, I assume you have managed to record succesfully during that time - what has changed??