I too have an Inspiron 9100 with exactly the same problem. After trawling the net looking for solution (yep, i tried all the adware removers/process monitors etc.) i found something NOT specific to the 9100 (it was for another dell machine with the same issue) that works a treat:
in your control panel
goto system
goto hardware
goto device manager
goto processor
double click on either processor
goto driver
click on roll back driver
you'll get a warning that it is and uncertified driver - click to continue
your machine will prompt to restart
when it start up thing are fast again!
Hope that this helps,
Roostrab