求助, 桌麵看不見start and desk top icon

my computer has issues. when turn on, desk top icons and start on left corner are dispear.but wall paper picture still show on back ground. use Control+Alt+Delte , Task Manager pop out.I have to use it to run the computer. I use F8 to use "last safe setup", but it does not work. my computer has Trojans and other virtus, it is difficult to clear. any suggestion? is there any key disfunction?
Thanks