jumping playback when recording 2nd track



I am new to the forum , have used Ntrack for several years , I have a pretty powerful duo core laptop running Vista Home , recently upgraded Ram to 2 gig , I use Tascam US122L as my soundcard etc , since I have upgraded to version 6 once I have recorded an initial track and then try to record a second or subsequent track the playback of what has already been recorded is jumpy whilst recording new piece, once new track is recorded the actual playback and quality of recording is fine but it’s hard to play perfectly when what you are playing along to is jumpy , I am using very little CPU 1-2% , have tried higher buffering on the Tascam but to no avail , have made sure internet connection is closed, also closed anti virus etc , can anyone help , I have tried all sorts of things , thought it might be graphics card but that is intergrated with the monitor so can’t disable it.

Any ideas please

You can run the DPC Latency checker, see link below. There are instructions to find hardware problems at the bottom of the page.
IRO sharing of soundcard can also cause problems.