How do you diagnose constant crashing issues, or system restore without a backup on ubuntu 10.10?

My recent installation 10.10 keeps crashing on start-up after working perfectly for one day.

Nothing new has been installed. I have just moved from XP so I would be very grateful if some one could please explain to me, as simply as possible, how to do the following...

1. How to diagnose the problem so it can be fixed, remember it may have to be before the log in.
2. Is there someway I can do a system restore to its original settings or something without a backup?

all hel开发者_运维技巧p is greatly appreciated.

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Your best bet in this case is to boot to the Live CD and then look at your logs on your harddrive. I don't have a live cd handy but the harddrive should mount under /mnt or /media. Once you have found the drive, look through var/log/dmesg (this can be sort of cryptic and var/log/messages to see if an error was written before the crash. The other thing that you can look at is doing a cd to the var/log/ directory on the harddrive and doing a ls -t --full-time, the top file will be the one that was written to most recently. Look in that top file and look for an error at the bottom of the file.

None of this will fix your problem but might help point you to the issue. If you think you've found something post it here.