its knackered...at least i think it is

its about 3/4 yrs old, its a 32 bit compaq effort running vista premium.. its given us ( the kids) good service till now.. but all the junk that they download ( minecraft ,torrents) its just had enough i think
tonight it seriously didnt want to let me go to google chrome so i used IE... urrg!!- then i heard it cry when i asked it to open 2 windows.. and it froze.. over and over
i have in the past deleted a heck of a lot of 'junk' from the programmes file.. more in frustration than understanding
i didnt get a disc with it ( why dont they do that anymore??) just wondered if theres anyway to reset it back to factory settings without and save my self the £45 that i know the shop down the road will charge ( was in there about 10 months ago for same reason) they stripped and reinstalled.
i seem to be missing a lot of 'plug ins'
theres no money for a new PC at the moment, single mum and lost my job 2 weeks ago!
any help would be greatly appreciated x