|Basically you need to consider a way to recover any data before you go to the next step. I use live cd's or bootable usb to access data.|
Then you have to locate your original disks or read doc's to find out how to recover your computer.
Might have to diag hardware issues if it isn't software. Like powersupply or ram or what not.
If you can't do all of that maybe a friend or neighbor might help otherwise you need a tech.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10