Unable to boot to home page

When logging on using Windows XP,SP3,and going to the welcome screen,
after typing in my password,I get the "loading Your Personal Settings "
message,then system hangs.After 15-20 power-offs & powering back on,
I can get to my Yahoo home page,afterwhich system runs fine.I can go to
Standby and be able to get back on but cannot logoff or turnoff without
encountering the same problem.Sometimes I don't get as far as the welcome
screen,getting a black screen or a welcome screen with no profile IDs.
If anybody can point me in the right direction to have a normal system again,
I would greatly appreciate it.