Hi there, if you lost your skype chat history (i mean all what you said on chat with your contacts) and now you see like nothing has been said, you might made a backup of your skype folder or configuration file so you can restore it.
What is the file where are stored Skype chat history?
C:\Users\yourwindowsusername\AppData\Roaming\Skype\yourskypename\main.db (if you cant see these folders, you may try enable show system folders and files (Google it)
if You use SkypePortable: SkypePortable\Data\settings\yourskypename\main.db
This is important folder, and you may backup it. Handy is to backup straight from Skype application.
Skype > Contacts > Advanced > Backup Contacts to File...
What is the file with skype configuration?
C:\Users\yourwindowsusername\AppData\Roaming\Skype\yourskypename\config.xml