If you do have spyware Spybot Search and Destroy is still a great program. When installing I do not turn on the resident protection as I find it a bit intrusive. Just leave the Tea Timer and resident protection unchecked.
Gotta go with these guy's both top decisions!!
Avast free initially and follow up with a malwarebytes right afterwards.
If anything is found use Avast again after selecting boot scan.
Follow up with Advanced System Care from IOBIT.com.
After your sure nothing in bios is behind the slow down.