Legends of Pegasus is considered to be an unfinishable game due to it's serious game ending bugs. However this cheat should allow you to get past the worst ones.

Here is the cheat to unlock all campaign missions in the game...

First go into the following folder:
C:\Users\%userprofile%\Documents\my games\Novacore Studios\Legends of Pegasus\profiles\

Then go into your profile folder and open User.xml with notepad or another text editor. Change the following lines to :
[actualCampaign]arthrox[/actualCampaign]
[actualEpisode]4[/actualEpisode]

You have now unlocked all missions in the campaign. :)

Notes:
The [actualCampaign] field will support 3 values: human / xor / arthrox
The [actualEpisode] field will support 4 values: 1 / 2 / 3 / 4