files module breaks on large files being uploaded or too many images imported

The Files module breaks when you upload a file greater than 2MB.All the files just won't open properly..it displays junk when u try and download a file.....Is there a way to restrict the user when he uploads a file which is too big so that the module doesn't break...and also when u upload too many images the files module breaks again....is there a max no. of images u can import without breaking the module and can this max be increased without breaking the files module...Would appreciate any help in this as our system crashed a few times already...