Vostro 3471, does not work properly

i bought 2 pc dell Vostro 3471 for professional office use. It is impossible to work with these products! Too low, access low, disk low, horrible! i don't know how it is available to sell this low quality if products and it is a shame for Dell! I always bought Dell products in my professional life. I had a bad experience with a printer 2 years ago but i let the doubt of the exception at Dell. This time, i'm totally disappointed! I called to have explanations and change the machines for an upgrade and was ready to pay much more to acquire PC usable but Dell refused! i can't explain this.