internet disconnecting every second (not isp problem)

My sisters comp is having trouble with the internet connection, she says every 2 seconds it disconnects, she has contaced the isp and they went over everything and still nothing helps.
Before i drive all the way over to her to get hijackthis logs and wait for help, Is it possible that this is caused by malware? or has her isp just fooled her?
Thank you in advance.