I need help with my computer?

i scanned my computer with norton and i found no risks but my computer was still lagging so i went on the norton website and took the next step by downloading the bootable recovery scan disk and i scanned my computer with that and it still found no risk so i scanned my computer with Spybot Search and Destroy for spyware and it found NOTHING. my computer is still lagging and sometimes it will speed up just enough for me to go online and look for support but it always happens to slow down again and sometimes becomes almost unresponsive. is there anything else i can do to help my computer speed up. is there something wrong with my norton settings? HELP!!!