Sound cutting out

I’m using Essential 4 on an Acer 5742 laptop (Windows 7 64 bit, 460M - i5) and have a problem with the sound cutting out half way through listening to a song.When this happens the only track that shows a signal is the Superior drummer track, the guitars,vocals etc don’t show anything in the mixer (and there is no sound).When I go to the VST audio system panel it shows that it has switched from my Tascam US800 driver to the Asio direct X full duplex driver.When I try to switch it back,I get the message “US800/Asio Open Fails”.
Does anyone know what is causing this and what I can do?

Make sure Release ASIO Driver In Background isn’t checked. Something’s taking the focus of the Tascam and it doesn’t sound like a multi-client driver. Might want to check if there is one at their site. Make sure Windows doesn’t use the device, also.

It only happens with songs recorded on this laptop and with this soundcard.I just played back a load of songs recorded on my old laptop (and recorded with a different soundcard) and they played back without problem even when there were a lot more tracks ie 1 midi track,3 vocal tracks,5 guitar tracks and one bass track (all with plug ins).
I also just made a new project and started to record a guitar with no plug ins and after a few seconds it stopped recording ie the recording signal just stopped even though the ‘band’ was still moving across the screen.After this happened I opened the ‘old’ songs (recorded on the old laptop) I had listened to 5 mins before and there was no sound and no signal apart from on the midi track (no sound here,just a signal).I checked on the VST audio syestem but it still showed the US800 driver.
When I was playing the guitar the audio interface was showing a signal (the green light was flickering)
Very strange and frustrating!
Any ideas anyone?