Hello there and welcome here
Please check following :
You have inserted the cable right, be sure it is completely in on both devices and do it in this way :
Insert the cable in the computer and insert the cable in the phone. look in the phone screen if it ask you which connection you will like to have, the choose the connection and the automatic driver installation begin :O)
Try to use another USB entrance in the computer and see if it helps, remember to check on the phone screen if it display anything where you need to accept the entrance.
Try with another cable, normally you can get them cheap on the phone accessories stores also online
In the manual here at page 14 on the following link they write :
"T-Mobile’s Customer Care offers responsive and knowledgeable customer support 24 hours a day, seven days a
week. It’s a free call anytime. Just dial 611 using your device or 1-800-937-8997 from any other phone.
You an also contact Customer Care through our Web site, by email, or regular mail:
Web site: www.t-mobile.com (click the link to Customer Care)
Regular mail: T-Mobile Customer Care
P.O. Box 37380
Albuquerque, NM 87176-7380"
Maybe you can try there
BTW I could not see anything on the manual about connecting to a computer unless you needed to restore the phone software, strange ??
Hope that helps
IF NOT then try to return here
Have a nice time over there
Please rate my answer