It took off 3 infections and it was still slow and...

It took off 3 infections and it was still slow and locking up when first booted up after running the stick the first time so I ran it again and it didn't find anything the second time but my computer is still slow at times and locks up for about 30 seconds before it starts working again, this was the main reason I wanted the stick, I understand this is windows 7 and the computer is old but I thought it might fix the problem.