OS X V10.7 Lion :: Mail.app Freezes And CPU Overheats?

Mail is frozen with the Properties window and an unfinished email open. It causes the CPU to overheat till 194ºF / 90ºC turning on the fan at a highly noisy speed. MacBook ProMac OS X 10.7.4Mail 5.2 I added a 4th IMAP account;Sent an email to check whether the account was properly set up;The mail was received without problems;Opened Mail Properties;Clicked on "Signatures";Mail froze;The CPU overheated till 194ºF / 90ºC with the fan spinning at high speed;The  icon didn't respond with Mail as active window;Switched to another app, then the  icon became active;Forced Mail to quit (it wasn't marked as Not responding);Realuanched Mail;The problem persisted;Restarted the MacBook Pro;Launched Mail;The problem persisted;Forced quit and relaunch the app;The problem persisted;Turned off the MBP;Swithed on the MBP;The problem persisted;Luanched Activity Monitor;Took a sample (No idea how to read, nor interpret it);Tried to "Quit" the app;Had to Force Quit Mail;Relaunched Mail;I was prompted to choose between restoring or not the windows;Chose not to restore the windows;The problem persisted;Relaunched Mail;The problem persisted;Forced Quit again from Activity Monitor;Relaunched Mail;Chose to restore the windows when prompted;The problem persisted;Created a new user (standard) account;Launched Mail;Set up an email account;It worked fine;Back to my user account;Relaunched Mail;The problem persisted; 

Info:
MacBook Pro, Mac OS X (10.7.4), Mail 5.2