Outlook express

Hi , just bought a laptop of my mate , worked ok up till now . Just tried to install modz-thunderbird , didnt like it , so uninstalled it , now back on outlook , so far so good ,but i go check mail all o'k' , next a popup tells me to install windows search , so i do , turn of lap top ( toshibs a300, xp) then when i restart , reg mechanic pup comes and goes, then my mates windows instant mess box appears , computer stalls at this point !, i pup arrow over messenger cose and click but nothing happens , even i try to shut it of the start up menu doesnt respond , no lights flashing nothin , i gota turn it of/on by the power button , HELP , what have i done ! confused, thanks in advance .......