Hi Not Tavo,
Congratulations on the purchase of your new iPhone SE! I understand you are having trouble syncing your new iPhone with iTunes on your PC. When you backed your old iPhone originally, did you do it via iCloud or iTunes? I would suggest setting your iPhone up as New, updating to iOS 9.3.1, and then syncing with iTunes. When you enable iCloud on your new iPhone, you will be able to see your contacts, calendars, notes, etc. I'll include a few resources below for you:
How to erase your iOS device and then set it up as a new device or restore it from backups
Erasing all content and settings will delete all of the data from your device, including songs, videos, contacts, photos, calendar information, and anything else. All device settings are restored to their factory condition.
To remove all settings and information from your device, tap Settings > General > Reset > Erase All Content and Settings.

After your device is erased, you should see the following screen:

Follow the steps to complete the setup assistant. When prompted, select "Set Up as New iPhone." Then tap Next.

Skip the Apple ID sign-in, in case the original issue was related to any of your content on iCloud.

After setting up as new, you will need to enter your Visual Voicemail password for iPhone (on carriers that support Visual Voicemail). If you've forgotten your password, contact your carrier to help you reset it.
After erasing and setting up as a new device, your device is now in a factory configuration. Re-try what you were trying when you first found the issue to determine if erasing and setting up as a new device resolved the issue. Content on the device might have caused the unexpected behavior.
- If the issue persists, you might want to contact Apple Support.
- If the issue is resolved, sync one type of content at a time back to your device. For example, if you had an issue playing music, add songs from iTunes and confirm that they will play. If your contacts weren't loading successfully, add the contacts back. After each sync, test to see if the issue has returned.
Sync your iPhone, iPad, or iPod touch with iTunes using USB
Take care,