Computer needs to restart because of a recent hardware or software update?

ok so A couple of days ago my computer wouldnt start it sed tht it was entering power save mode and then jus went black wen i pressed one of the monitor ons it sed tht it is in power save mode and that i shud press sum other ons to start it up...i did tht and it didnt wrk...so i called my technician frend and he told me to get to the boot menu during start up and select start windows at last best known configuration or sumn like tht so i clicked it and it wrked (my hard drive is split between xp and vista btw so wen im startin up i choose which one i want to go in...this happened with vista but it wrked fine with xp) anyway...i used it fine last night and stuff but today wen i tried to turn it on it wudnt p this blk screen with the comp info u always see wen ur pc is startin up and it was tellin me to go to setup menu and such and if i didnt click on anything it wud jus go bk to the power save crap and go black so i restarted and pressed F2 i think and went into the setup menu... now this is where i feel i screwed things up cuz then wen i went into the thing it had a rong date and time and **** so i figured if they kept pushing me to go to the setup they must want me to change sumthing so i changed the date and time to the current date n time and now i wished i hadnt cuz wen i come out and restarted the pc...it boots up jus to where u see the microsoft loading bar with the green thing in it..then it jus stops and restarts itslef, tellin me that i need my windows cd to restart my system cuz there has been a recent change in my hardware settings or sumn like that.... now i feel like this is my fault cuz now it wont evn go into xp either...cud sumone tell me what is likely to happen after all this..am i going to lose my stuff on the pc? i dont have a windows cd, i realli dnt kno where tht is, is there a way i could get around the 'i have to restart' thing?