Unable to download music from iTunes

I'm having a major problem with my iTunes and I'm hoping someone can help. The first sign of trouble was on last Tuesday. I purchased three songs. Two of the songs would only play for about 45 seconds. Then the last song never downloaded. I emailed the help desk for i tunes and they refunded my account. So I purchased another song and the same thing happened. The song only play for now 30 seconds. Once again I emailed helpdesk. Once again they refunded my account. However they are not offering a solution to the problem.

So again two days later I try to buy a different song. Now in the middle of the downloading process I get an error -69. I checked the internet and help section for i tunes. All the information I found was for trouble syncing an iPod. I'm not trying to download to my iPod. I want to download to my computer. All the songs I have in my library have been purchases thru iTunes. I have over 3,000. Can someone please please help me....thanks