erratic startup, missing files??

when starting my system I get an error message:
c:\windows\system\vmm32.vxd not found. The file is
located in c:\windows\system\.. when I reboot and
select step-by-step dialog. I get as far as:
c:\windows\system\umaxis11.386.exe not found. Thisalso is found where stated. Occasionally, my
desktop icons become scrambled?? I can use the
computer after single stepping but when shutdown I
get the same errors. Registry????