Engine problem. Need help please

[Aleks]

I'm 18 years old guy. This summer I bought my first bike, 1980 XS400. I had very little knowledge about engines. I have done a lot of mechanical work with my own car, but never had the courage to touch the engine in fear of messing something up.
Now I started stripping the bike down, to get the frame and everything else fully painted and restored while it's winter.
I was being a little bit stupid and was thinking about checking inside the cylinder head. Bad idea. Actually wanted to change all caskets in future, because while disassembeling some engine sidecovers, found out that the gaskets are in bad shape, so was thinking about changing all of them by myself.
I removed the cylinder head cover, possibly loosened bolts in wrong order. When loosening last bolt from the top, there was pressure coming out and pushed the cover up. Later after assembling it back on there was no compression and no resistance on kickstarter.
I hope there is nothing serious.
At least now I know not to touch anything before doing a lot of research.

And before it was running fine. Sometimes had problems, wanted to stall, but I was thinking there's problems with carbs.

 

[Aleks]

Does anyone have any idea, what I messed up?

 

[NewHavenMike]

Yea, read the manual (available here) and figure out how to get it back together.

The engine ran fine, no need to open it up.

 

[buztabuzt]

You're description is hard to follow and you post no pictures.

As Mike and your momma always say: read the instructions first. Then read them again. Then take pics. Then do your work. Then if you still have questions post a specific question with detail of what happened, symptoms, etc

Godspeed!