There is a problem which was announced two days ago. Many users are reporting "missing contacts.".
I suggest you report it on the status page. If enough users do this they may escalate the issue
Check the status page for an eta on the fix.
https://status.live.com/
You may be able to view your contacts in the mobile view. To access that....
- Login to your account
- Follow this link http://profile.live.com/contacts?bfv=um.
- Click the word "PC site" at the bottom part of the page
If you want to switch back to mobile simply log onto m.mail.live.com
If the above doesnt work
Try a different browser, Optimize your browser, and try disabling the flash plug in. It has worked for some users
Try refreshing the screen using F5 (or its equivalent)