Your wireless modem may be pulling you down there since no pc takes over a solid minute to fully load past post tests and OS loadup. Do you have other hardwares like a printer connected? If it isn't hardware the systems files may have been hit by something(Adware-spyware-virus-malware).
The last item would be an internal not external problem with memory, cpu, or even power supply circuit or cmos issue where voltages have been reduced. A good freeware for monitoring that stuff can be found at:
http://www.tucows.com/preview/226226 That's one place for SpeedFan 4.20.