I only have a USB cable to charge my tablet and I plugged it into my laptop to charge and a little red X shows up on the battery thing. How can I charge my tablet?
A computer's usb port does not supply enough current to charge your tablet. The tablet takes roughly 1A or 1,000mA to charge, a desktop's usb port only puts out about 500mA. Some laptops just can't provide the specified 500mA and will not charge it at all. YMMV
You can charge it though, only very slowly, AND the tablet has to be completely turned off.