VB .net alternative to check if file exsits

i have been asked to make a program that will show a warning on all computers in our school.

i have made some simple forms that only appear when a text file appears in a shared area on our network. It works but the more instances of the program checking the server the slower they get.

is there an alternative i could use rather than if file exist then show a form?

if you need more details please ask and ill try to provide it.

Thanks