1) HTC doesn't void the warranty for rooting (unless rooting caused the problem you're trying to get fixed under warranty).
2) Not reading the card has nothing to do with rooting. Put the card into a card reader and see if your computer can read it. If not, the card is bad. (If it's a SanDisk, go to
SanDisk Online RMA Request, fill out the form and get it replaced.) If the computer can read it, the phone may have a bad SD card port or there may be a problem with the phone's firmware.
@Deborah:
If the phone won't read the SIM card, you won't get 4G, so it's the same problem. Bring the phone into the carrier and have them check it. (You might just need a new SIM card.)