my sonar sometimes doesn't record

hey there. i have sonar3 producer edition. it worked perfectly on my old computer. now i installed it to my new one and i keep getting the following problem: when i make an audio-recording, the waveform preview shows me that i'm actually recording a track. but when i stop the recording it just dissapears in most cases. i think the longer a recording is, the more often it dissapears. is there any cache function i didn't see or anything else in the global or audio settings? (i got read and write caching enabled, but get the same result when i disable them). thanks for helping, sascha