Windows xp pc wont allow me to do anything?

i have ran numerous malware and virus scans and removed all threats they come up with. one wont let me delete or move to vault. when i run in safe mode i keep getting svchost.exe- application error instruction at "0x001a624b" referenced memory at "0x000000000" click ok to terminate or no to debug. in safe mode i can run the mal ware scans but in reg boot up i can not click start or open any shortcuts i cant even tell the computer to power off or restart.