Can't soft reset or go into bootloader

[jnmat]

I recently got my HTC Touch Diamond digitizer and LCD replaced by a local shop after Vodafone UK refused to fix the non-working digitizer under warranty as they claimed that the phone was water damaged, which wasn't true as I got it fixed finally. Before the repair the phone will restart by itself after pressing the red soft reset button. Now after pressing the button it will just switch off, and I will have to press the power button to switch the phone on again. Furthermore, I cannot go into bootloader as pressing and holding the combination buttons 'vol down' and 'centre key' together with the reset button will only switch the phone off.

Has anyone experienced a problem like this before? Where does the problem lie actually I wonder?