Not if you haven't changed any hardware. It should just activate over the
internet. However if it does not, use the Activate by Telephone option,
it's a toll free calls and usually takes only a few minutes.
No, you shouldn't have any problems re-activating, so long as you haven't
drastically changed any of the hardware. Have a look at the following
article by MVP Alex Nichol:
Do not get in a hurry to reactivate. Use the system a
few days and make sure you got the install you wanted
before activating. If you activate several times in a
short period you will be directed to activate by phone.
This is never a problem but can take several minutes.
Save yourself the hassle.