monitor going BLACK after changing screen reesolution

[slugonice]

i changed the screen resolution for UBUNTU from the default 800x640 to something higher
after applying, the screen went BLACK

how do i restore to default settings?
or solve this problem
please help
im new to linux

[lingwen]

reboot the computer go into the grub loading page and you should have a repair option go through all that then reboot normally and if you want to change resolution try to not put something too high for your monitors capacity

[slugonice]

my monitor can support 1000 something resolution on Windows
why cant it get that on Ubuntu?

how do i make it get higher resolution without the monitor going black?