I am now trying to charge my new Samsung Galaxy tab since morning and it keeps flashing on me. No signs of it being charged. I am unable to switch it on. Please, for how long is it going to have to be charged before I can turn it on for my usage?
I realize that this is too late to help the OP, who apparently couldn't be bothered to follow up, but for future readers that might come across this in a search...
Samsung products are pretty picky about the chargers they will recognize, and there can be several problems using "known-good" chargers.
Most after-market chargers are designed for Apple devices, and will not quick charge most Android devices without a special cable or adapter. But even with this special charging adapter/cable, some chargers won't work for Samsung even though they might work for, say, LG (I have this scenario, so I know about it).
Also, most USB ports, and many chargers, cannot supply more than .5 amps, which is not enough for many phones or tablets.
So, the bottom line is to always keep the original charger and cable to test the device, and if you can, try to get a replacement before you need it, so you can compare it to the original to make sure it works. Otherwise, if your original goes bad, and you get a replacement that doesn't work also, you'll never know where the problem lies.