which antivirus was instaleed... NAV and McAfee creats problem in this kinda things...
try one thing...
http://sysinfo.org/startuplist.php
this website contains huge list of all start-up items...
if u remember what what things u disabled then we can tell ya some details...
if u can run in safe mode then also scan for spyware....
and if tht PC supports DEP then disable it... sometimes in certain conditions this also creates problem (i heard but not sure as i never had problem with DEP)
to do this
open boot.ini
and chage the /fast detect /NoExecute=OptIn
to only
/fastdetect
all the best...