Stuck home screen unable to get to main page iPhone 3G

I recently updated my iPhone on iTunes (a friends) and ever since, every time I shut off my phone overnight & turn it on the next morning, it gets stuck on the main screen where you slide to unlock...only I cant do even that. I cant shut if off, manually restart, nothing. So, now I feel like I cant even shut my phone off ever!! The only way I got it to work last time this happened was to plug it back in to my friends iTunes....but I cant have this not work until I see that friend again. I have it plugged in but I cant get past this screen. Any suggestions?
HP Compaq