When I boot my computer it comes up to the apple logo and has the loading wheel beneth it then after a minute or 2 a bar appears underneath the wheel. The bar stays for a while then leaves, it does this 3 times then the computer shuts down. I then proceeded to boot in single user mode to see if I could find the problem. Every thing boots fine until it tries to mount Disk0s2. It fails and says errno:19 it tries about 7 times and then says mounted read-only. I then try to boot from single user mode. It then says Disk0s2 I/O error 3 times. and powers down. How do I fix this. I have no startup disk.