Vista Booting issue

Hi All

I have a Acer Extenza 5620 with Vista Business. When I start up the PC it boots fine all the way until it needs to display that Vista logo and the user select screen. Instead the screen just shows as black with the mouse pointer. I'm able to see hard drive activity, move the mouse and enable num lock and stuff but if I try pressing Ctrl+Alt+Delete to get the task manager nothing happens. If it's left for a while the screen saver appears. Very weird I know. The biggest problem is that I dont have any recovery disc or partitions. Please assist.