First thing is goto bios menu(By pressing F8 or del key while computer starts up) press Restore to default and press F10 and press yes,
Second thing is You might use a good antivirus,
third thing is comparatively vista is very slow try to format your OS .
Press and hold control switch + r
There you can a new window called run
Enter there "MSCONFIG" ,Press enter
There will be a new window goto startup and untick all unneccessary startup (Which will start programs automatically in starting) items , press apply.
Press and hold control switch + r AGAIN
enter %temp% and press enter
There will a new folder opens
delete all files in that folder.
Or
you can you a junk file cleaner use CCLEANER for free
click here to download it
Thanks.