Internet Cable Speed

when your internet's going extremely slow, and you've tried everything, is there an app to find the culprit? usually my internet is blazing fast, but not tonight i ran all the usual AVG, and malware virus type scanners, and nothing came back unusual did the windows and manufacurer's updates etc, but it's still going slow .. i can't even streem a movie tonight from netflix, nbc, youtube etc so is there a way i can see if it's my ISP's fault (short of normal dsl report type speed tests) or see if maybe someone is hacking in and stealing my bandwidth ... i doubt that that is the case, as i use a wep password but it's slow on all my computers tonight, and it never has been before i did try restting the modem (didn't help), and router .. but ya i guess one of those could be biting the dust ... well if it's still bad tomorrow i guess i'll call the ISP ... thanks guys