Discounting is effectively removing the interest cost. The higher the interest cost, then the less worthily the investment.
Higher discount rates certainly do not mean a negative NPV!!! The NPV will be lower, and therefore may end up being negative, but it is certainly not always the case.
Again, you really need to watch my free lectures (and it might help you to watch the Paper MA (was F2) lectures on interest and discounting, because, again, this is basic revision of Paper MA).