This PC can't run Windows 8

[ApolloTheDragon]

Alright So my pc has not been working right for pass 6 weeks AVG cant fine any thing wrong with it. Not running at Full speed.

But any ways I run Windows 8.1 and try to put 8 back on Every time I put 8.1 on it goes to hell and one know why I can't seem to put windows back on?

Says this "There isn't enough free space on the system partition."

 

[Alpha3031]

C: drive is not big enough, try deleting some restore points etc

 

[ApolloTheDragon]

I have 634 GB free of 931 GB of space left how is there not enough space