PowerBi Beginner Queries

anagha_sharma Power BI Desktop is the primary tool for creating datasets and reports. Power BI Service is most often used to share published reports and dashboards with others. That said, you can do data transformation in the Service using Dataflows. Now, you won't have all of the modeling capabilities of the Desktop, but you could for example create Dataflows in the Service that do all of your data transformation and then simply connect to those dataflows from Power BI Desktop to create your data model. 

Hard to say if you are doing anything wrong. Would need to know how much data you have, the transformations you are attempting, etc. Would also need to know the spec's of your hardware. It is generally best practice to do heavy transformations within the source system and keep transformations in Power Query to a minimum in order to maximize performance but that's not always possible. 

Power BI Desktop does save the PBIX file regularly and you can sometimes recover the file. Might be best if you use Advanced Editor in Power Query Editor to copy and paste the underlying query into something like Notepad.