HTC Desire :: Screen Randomly Freezing / Is It Hardware Problem - Software?

I have an unbranded, rooted Desire running 2.2. My screen randomly freezes and cannot be used from several minutes, up to an hour or so. There is no set pattern to when this happens. I have done a hard reset, which has not sorted the problem. I am currently using the phone without the memory card to see if that is the problem, but the screen has already frozen briefly.

All the buttons work properly and any function controlled via buttons works when the screen is non-responsive, so it is not the phone that has fozen just the screen.

I have had the phone for 6 weeks. Is this likely to be some sort of hardware problem or software?

Has anybody else had this problem (couldn,t find anything from a search)?

A touch screen phone where the screen does not respond to touch is a bit frustrating!