You need to tell us exactly what you've tried, otherwise, we are all guessing what you've tried. "Everything" is quite a broad term. You need to narrow it down for us. Regardless, I'll take a stab at answering...đ
Have you tried a different USB port on the PC? Some are NOT created equally and some may not be able to supply enough current to the device for it to be recognozed. Do NOT use a USB port on a keyboard or unpowered USB hub...these may be able to work with an iPod (requires much less current than an iPad 2) but may not supply enough current for a full-sized iPad.
Have you inspected the 30-pin port on the bottom of the iPad for dust/lint/etc? These ports can get junk built-up/lodged inside of them. Clean it out with a clean toothbrush or similar.