If you lost your content after upgrading to 1.2.0, look to
this thread in mailing list archives and follow Next message link until you find the
solution.
In short: it is caused by <TyposcriptObjectPath> tag in your DS. If it is present for ce field, you will not get your content elements. Remove the tag. More details in that post.

Everything was fine, then computer crashed and restarted without warning.
Now get these errors in the tree, and can't add new contact:
Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in C:typo3htdocscmseigt3libclass.t3lib_db.php on line 796
Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in C:typo3htdocscmseigt3libclass.t3lib_db.php on line 796
Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in C:typo3htdocscmseigt3libclass.t3lib_db.php on line 796
Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in C:typo3htdocscmseigt3libclass.t3lib_db.php on line 796
Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in C:typo3htdocscmseigt3libclass.t3lib_db.php on line 796