I just had the same yellow triangle myself! I had a few problems with it, so i reflashed galaxy cubed. The computer was acting up and i ended with the yellow triangle. So, turn off the computer, then turn it back on. Wait for it to fully boot. Turn on the tab, wait for the yellow triangle. Plug into the computer. My computer beeps when something is plugged in. This lets you know the computer recognizes the tab. Then open heimdall the folder, run zadig to install the drivers. Close out, open heimdall front end and reflash. This is exactly what i did yesterday. A blue line should apear as it progresses under the yellow triangle.
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