There have been quality control problems with some DSTT's. If you get a good one, it's a great cart. That's why I always recommend that people ask their seller to test it before sending it out (it's in the seller's best interests to make sure the cart works before sending it). Also, make sure that you can replace it if you get a bad one.
Athang, it definitely sounds like you either have a bad DSTT or a bad microSD card. First try reformmatting your microSD card, and insert it without installing the kernel. You should get an icon that says "Menu?" if it detects a card with no firmware. If you're still getting a "No Card" icon, then try to borrow another microSD card and insert it. Again, don't worry about putting the firmware on it (yet). If it still says "No Card" then your DSTT is probably bad. See if you can exchange it for a new one.
-Bri