Fidelity has been great with working with my accounts. So simple to set this stuff up and roll things over.
I agree with the other people - open a Roth 401(k) and roll your current 401(k) into it. Forget it is there. Then go ahead and contribute to your new plan. It doesn't really matter where your money sits or in how many accounts... only difference between standard and Roth is when you pay taxes on the money.
My wife and I have two traditional 401(k)s, Roth 401(k), two Roth IRAs (unable to contribute thanks to income limits!), and now a SEP IRA, not to mention an investment account, two 529 college savings plans for the kids, and 4 checking and savings accounts (personal, home loan, one each for our businesses.) Yes our money is a little spread out, but it is just how things work. Keep track of it and you are fine.
Again, I cannot say enough good things about Fidelity. They've truly done a good job and make account tracking and investing very easy.