Whenever I startup, restart, or turn my computer on after hibernation my computer lowers its resolution from 1280x800 to 800x600. What's causing this and/or how can I fix it.

What operating system are you using? Is it Windows 7? Because my friend was having the exact same problem, fixed it when he changed over from the beta

I have Windows Vista.

Is this a laptop computer or is that a separate monitor? If it is a separate monitor, make sure your monitor is running by the time Windows is starting back up, otherwise there is a chance it may be unable to detect what modes it supports.

I am using a laptop.