new email settings

After getting tons of emails I set two accounts to the new settings. I could receive or send mail, but not both. Called tech support and got no help. I was actually told it was an Apple problem and I would have to call them. I thought I had it figured out on my own and all was actually going well. After a robo call I changed all four accounts to the new settings. We started getting error messages and email crashed a lot. It slowed down the whole computer and now we have some problems with missing files on the actual computer. For awhile we couldn't even get the computer to reboot or start up at all. After turning off the computer and not using it for 24 hours it now works, but we cannot use Apple mail. As soon as we do the whole thing crashes. We live in a very rural area and are "lucky" we have DSl at all. Verizon tech support is worthless and our whold computer has been comprised.