Pity you are unable to answer even a few of Methyl's questions. Waiting until July for your neighbour's son, might be too late to 'save' your computer.
I am thinking that, in an attempt to rectify your problems, you may have been onto a Scam Scanning site which might even have put some malware into your computer to produce fictitious viruses, which it will remove at a cost
You say you have installed Avast. What has it found by way of 'nasties' ?.
Please consider matters further and posting again in this thread might be worthwhile.
Hans