Computer operating system re-installing?please help!!!?

please read this whole thing. i beg of you. last week i used a pen drive and from then onwards my pc became insanely slow. these are the things that happened and are troubling me. please read them. 1. pc became too slow. it takes about 15 minutes to start and infinite amount of time to shut down. 2. even a... show more please read this whole thing. i beg of you.

last week i used a pen drive and from then onwards my pc became insanely slow. these are the things that happened and are troubling me. please read them.

1. pc became too slow. it takes about 15 minutes to start and infinite amount of time to shut down.
2. even a small program like paint takes about a minute to open.
3. google chrome doesn't work. mozilla takes a long time to open. somehow i am able to type this in mozilla.
4.i lost my task manager. i am getting "disabled by administrator".
5. i have also lost my registry key window. i am getting the same window.
6. i've read about how to get them back. i tried windows group policy but that doesn't work
7. i tried system restore, but too bad the check point isn't available. above all system restore is greyed out.
8. i've tried opening in safe mode and doing a restore but that doesn't work.
9. at last i've decided to format whole of my pc.
10. also in about a day i got about 1000 temp files and there is no way that i can delete them.
so i downloaded a iso format windows xp file of the internet. and then burned it in another computer and brought it and used it in mine. i've seen youtube tutorials on it,. but i am not sure why the cd is not running in my computer. i've tried it in other computers. it works fine. probably i am unable to make a bootable disk. or probably my cd/dvd rom is faulty.

so now what do i do? i dont know how to get my pc formatted with these circumstances. yes i do have a pen drive. so can i use it and make it a bootbale usb and use it to do this job. please help. don't give me links to sites like youtube coz they are taking about 10-15 minutes to open alone and yet another 5 minutes to buffer. please type it or at least paste the stuff. i am in a dire need. i know i have so many mistakes in the above said description but i can';t go back and correct them coz this pc is toot slow.
3 answers