Windows supports OHCI firewire protocol…no drivers needed. Try turning off all other firewire devices.
A bad cable can cause the problem… I have 2 cams that have bad firewire ports.
Are you viewing on a TV? If not, your problem may be with your graphics card, Windows or a Media Player setting that will display at 1/4 or 1/2 resolution.
It is likely that the tape has broken timecode, caused by rewinding the tape and viewing the video and then stopping the the playback after the video ended, placing the record drum on blank tape which will cause the timecode to start over.