its about 4 months & there will be lot of data read & write with your HDD, so also system restore wont hold all the restore points, it will remove the old one when its make new restore point after some time (by default 10 to 12 % of you drive will be used for system restore)
The problem with the failed restore point attempts is with Norton. All that needs to be done is this:
1) Open Norton Antivirus
2) Click SETTINGS in the upper right hand corner
3) Uncheck the box that says NORTON TAMPER PROTECTION
4) Select the time frame that you need tamper protection to be off
5) Your restore point selection should not fail now.