my bluetooth and usb both work yesterday, but today when i tried to connect by usb and download and compile, the software file doesnt change. so when i check the link step up and clicked usb connection, the message log showed that "checking NXT battery level high enough (>6.00V) to continue" and it just couldnt connect.....is there anyway to solve this problem...this is emergency..i need it to work by tomorrow ]:

Try to put in a new set of batteries. If your battery level is below a certain point Robot-C will automatically cancel a download until you replace the batteries and the NXT has enough power to properly understand the code. Low battery level can effect a lot of things on your NXT, including slow or random speeds and shorter distances than you specified in the code. Robot-C just reminds you of those problems when you're trying to download a program-just to make sure everything runs right.