Start the computer and immediately start pressing the F8 key, once per second till a selection screen loads. At the selection screen, use the up/down arrow keys to select Safe Mode, then press the "Enter" key. If it starts in Safe Mode, try using System Restore.. If System Restore doesn't work from Safe Mode, then restart the computer again, using the F8 key at startup and this time, select "Last Known Good Configuration". Press the "Enter" key, then follow the prompts to restart the computer to a time when things were good.
For other options to fix the error you're seeing, see the links below:
Hope this helps.
Don't know if it as coincidence but yesterday I uninstalled McAfee Anti Virus and when I restarted my PC it wouldn't boot up. I was asked to open the start up repair which I did but upon running this is said it couldn't repair it stating -
"No OS Files Found On Disk" with the Error Code 0x490
How can I resolve this without losing all my data, hope someone can help!!