Hello - need help!

While back I purchased a Dell that came with Win Millenium installed and
included a CD upgrade to XP. All has been working fine, until a few days ago
when I added 512MB of memory to the meager 256MB. After I installed the
memory, a window popped up prompting me to activate windows with Microsoft
within three days. Toward the end of day 3, I found myself locked out of
windows. At the log-in I was prompted with "Do you want to activate now?"
When I pressed "yes", my empty desktop appeared with a blank window,
entitled 'windows product activation' with no cue whatsoever on how to
continue. When I cclicked "no", I was promptly logged off. I should add, I
never was prompted to activate windows to begin with since its intial
installation.

Dell was unable to solve the problem and referred me to Microsoft. I paid
Microsoft a $35 service charge (Dell wanted $95). But no immediate help
from microsoft either. The technician there recommended installing a new XP
upgrade CD which should arrive any day. However, he could not be sure a new
upgrade CD would work.

Has anyone experienced this problem and discovered a solution to it?
Thank you in advance,
Vega --