This instruction may apply to Tmobile USA users. In my search for a Do-It-Yourself fix, I searched internet for several days to no avail. Amazon.com sells Touchscreen and Digitizer but their results were inconsistent; the replacement also required time, skills & instruments that I do not have.
Tmobile: Tmobile (800 number) asked me to restore OS, but it did not work. They asked me to take it in the Tmobile store. The store associate looked at the phone, but they did not want to do anything with the phone as I did not buy my phone from Tmobile - they directed me to HTC or a local repair shop. Local repair shop was going to charge $100 for a repair and turn around time of 15 days.
HTC : I called HTC (888 356 2375). As the phone was still under warranty, they offered to take a look at it & repair it. HTC also mentioned that if the warranty is void for any reason, they would charge $39.00 for a triage fee and call me to confirm the repairing cost (in addition to triage fee). HTC mentioned that any illegal softwares found on the device would void the warranty.
Restore to OEM:
I had to restore my softwares to OEM as I installed a newer radio, HSPL, MAGLDR, and a custom windows ROM. To do so, following ROM was flashed :
Flashing above ROM restored ORIGINAL OEM radio, SPL, and Windows ROM. It also removed MAGLDR.
After restoring softwares to OEM, I sent the phone in. The repair was done by HTC without any charge. After sending the phone in, I had my phone back in 1 week - fairly quick service compared to all the other options I had at hand.
In the process, HTC kept me informed via email regularly. I talked to several HTC reps and they were very accommodating and courteous. I mentioned to HTC that my battery drains very easily. Promptly (in 2 days), HTC sent me a replacement battery for free. They mentioned that as long as the phone is under warranty, they will replace accessories ONCE for free. I will buy HTC again despite the touchscreen problem.
Immediately after receiving the phone, I installed newest Radio, HSPL, MAGDLR & my first Android NAND [HD2_Core_Droid_Desire_HD_V1.4_NAND_ONLY_LEO1024_TO US]. The android ROM is rocking even harder straight out of box.