It sounds as though you've got serious problems occurring as soon as your PC boots into Windows. As masterhacker suggested, you may have rogue/invalid registry entries referring to applications or files that no longer exist, and using a registry cleaner may help.

However, my first port of call in this situation would be msconfig, which can be located by going Start - Run - msconfig and hitting enter. Under the startup tab there will be references to all the applications that run on boot - removing non-essential items will increase performance and possibly even alleviate your problem. Common things that run include media players, printer drivers, photo suites and so forth. If one of these programs is trying to do something on startup (i.e. install a component) then it may just be responsible for your problems.

Have a look in msconfig and remove non-essential applications from startup - if in doubt, post what comes up here and we will be able to tell you what should be running and what you can do without.

John