Catty
If they are stored on the computer there may be a way to restore them
Go offline and log off then logon again
But do not go online...open your address book ...Has the addresses changed to the email addresses? If yes then Log on with the address book open ,should work now?
If the answer is No change. then Close everything
Next open the Start menu check first in the Left hand column that System Restore is not on the lists ..If Not then click All Programs> Accessories>System Tools> System Restore
Click on this and select
Restore My computer to an earlier time then click the "Next>" button
Next a calendar will appear note some of the date are in
Bold letters...These are the restore points I cannot say how far you can go back but In your case go back to whatever day you were able to send out an email to one of your comtacts on the list ...say last Saturday or Sunday (10th or 11 th ) is either day marked up in
Bold letters? if No then go backwards to the First day which is
Now Click on it and there'll be a message like Software distribution 2.0 display in the frame or if you have installed or removed a program on that day info on this will be displayed as well
But all you have to do catty is look beneath the Calendar for the "Next>" Button
Clicking on this will Start the "Wizard" Takes a few minutes, then You reset the computer
Now Log back on and there'll be a message saying its been reset to an earier time...Can undo it if you feel unsure by going to the restore point before the current one ...It makes one for the "restore" by default
Go online and Go to your email program
Now look at your contact list , has it been restored? If so you should be OK from Now on otherwise we need more assistance
And here is the long winded guide form Microsoft with Screenshots 
