When an exclamation mark (!) appears on the display, press the following keys in the the following order: Volume up, Volume down, Power button, Volume down click here or google for: 'htc 8x factory reset exclamation mark'
Thank you all for your help, it seems the phone has water damage . Examined by phone repair specialist advised not worth repairing .We have been duped by the seller bought on gumtree by my teenage son. No contact details , the phone number given goes to answer machine. Lesson learnt thank you again
Sorry for the delay in replying