Coffee is so weak it tastes like water, not at all like my tassimo. Normal?

SOURCE: Braun Tassimo Coffee

It's most probably from the overflow which is situated behind the splashback. When the machine leaks from there it generally means that it needs to be descaled. You can use a general descaling agent powder. dissolve it into the water container filled to max, with the cleaning disc run a few cycles with 15 minute gaps between each cycle. after it should be fine.

SOURCE: Weak Coffee

Yep, it's the one inherent flaw in the single serve machines - someone else decides what 'the perfect cup of coffee' tastes like.  Quite presumptuous, actually.  
Solution I found to be acceptable:  Buy only the extra bold flavors (there's about 5 or 6 varieties) and brew using the small cup size button.  Yes, you only fill your mug about 3/4 of the way, but at least you get a decent cup of coffee.  
The ONLY flavor I found to be strong enough when brewing with the large cup control button is DOUBLE BLACK DIAMOND...the rest is crap.

SOURCE: lights keep flashing on my tassimo machine

I know that if the water reservoir is empty or the reservoir isn't properly attached all the lights flash until I correct it. I think the first time I powered on my unit all the lights flashed as well but went away after I put a coffee disc in.

SOURCE: NOT SO GREAT COFFEE GROUNDS!

Might there be some stuff crusting the dispanser vent? Did you clean it regularly? If you've not done that, this is what you do:

1) Open up the lid where the T-Disc is supposed to go.

2) Take out any moveable (not breakable) object, for instance the thing that punctuates the T-Disc(its made of two parts stuck together) and the T-Disc holder.

3) Take 'em apart and put 'em into your dishwasher or wash it by hand.

4) Wipe the entire T-disc area with a damp cloth, make sure nothing stays there that isn't supposed to be there.

5) Put the removed and cleaned parts back very carefully and watch out that they are exactly in place, if in doubt wheter they are fitted correctly, just shake them a little. There should be no movement other than up and down.

6) Enjoy your coffee!

SOURCE: Senseo machine has started producing very weak coffee

try descaling the machine first, build up may be causing problems. its in the direction book on the senseo site.
If that doesn't work
Call senseo at 866-4-736-736 866-4-Senseo and describe the problem.if you have purchased or received it as a gift less than two years ago they will send a new one FREE.