Again what do I do to buy a good DSLR and avoid the Problematic ones?

Put aside the different types of DSLR and SLR, that's a whole other matter.
Every camera I check and read about it must have a problem Nikon d90, d5000 or even the d7000, canon 500D. The list goes on. There are always 5 star reviews but the one star reviews that I read points to bad cord problem, shutter problems, "ERR" message, camera shuts down for no reason and never works again. These are not individual accidents, as I read, many consumers face these malfunctions. All this aside, there's also the problem of customer services where they never help you, you have to send the damaged camera on your expense although your warranty is not expired yet T.T

After the research I did I'm afraid that I might be one of the unlucky ones and I'm very scared to get a new camera and invest in it through lenses and other stuff just to discover a week later that it doesn't work anymore.

What can I do? Isn't there a DSLR Nikon that doesn't have any problem and only got 100 positive reviews?

ANYTHING that is man-made will have a certain quantity that fails (there's no such thing as perfection). Nikon and Canon seem to have better customer service than other brands. I have owned Canons for over a long time and never had any of the issues other complain about.

Also, a lot of bad reviews when further explored are "user error"… It was dropped/smashed/liquid spilled on it, not reading the user manual, not following proper instruction. It sounds better to say "it just quit working" than it is to say "I accidentally plugged it into a 240v circuit"

Problem with reviews is that anyone can write them even if they don't own the camera, in other words people love to lie.