Recently had to reboot my computer
I Have had to reboot my computer and when I plug phone in it try's deleting everything before syncing i have already lost alert and ringtones any help would be greatly appreciated.
iPad, iOS 8.1.2
Rebooting a computer shouldn't make any difference, or do you mean that you've reinstalled the OS on it ? If you do then your phone will be seeing it as a new computer (iPhones are designed to only be synced to one computer at a time). See if this user-tip helps you sync to it : Syncing to a "New" Computer or replacing a "crashed" Hard Drive
Some of the steps on that page have changed slightly (it was written for a previous version of iTunes) :
5, is now File > Devices > Transfer Purchases
6, 'Reset Warnings' at the bottom of the phone's Summary tab in iTunes
7, File > Devices > Back Up
8, File > Devices > Restore from Backup (or Restore Backup button on the Summary tab)
For the tones, add them back from your backup of your downloads/library that you took before reinstating the OS. If you hadn't backed them up (and assuming that they are iTunes purchases), and if they are still in the store and you haven't moved countries since buying, then you can try contacting iTunes Support and see if they will grant you a redownload : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page
If you don't have copies of your music then there are some programs listed half-way down this page which can copy non-iTunes purchased content back from a device (iTunes will only copy iTunes purchases) : Recover your iTunes library from your iPod or iOS device