There are a few solutions in the FAQ thread and many in this section of the forum.
The most common culprits are running 3rd party tuning softwares like GPU tuners and over-clockers turning those off or in some cases you need to uninstall them. Malware and virus scan softwares cause a lot of problems. Out of date display drivers, although I think that has been mostly resolved by the required minimum drivers Oculus has now. Having "special" characters in your file path was causing issues but I think that has been resolved.