ANOTHER NEWBIE ???? HELP!!!

:/ I have finally got my 1st build pc finished. Yes it was my psu that was bad. nNow my problem is, after I boot and everything is loaded Windows XP H.E. freezes or is running so slow that the system is busy and I cant open anything. Any ideas what could be wrong???And my second question, how do I find the temp for my computer. Do I need software to moniter the temps.
Thanks for all and any help!!
FANCY02