You don't need new computers. You just need to clean up the ones you have and moderate your usage habits to prevent bad things from happening in the future. Step 1 I would recommend a physical cleaning just to make sure your CPU is not throttling. Take the side panel off the case and get some compressed air cans from Best buy/Radio shack/etc and spray out the dust inside the case paying special attention to the CPU cooler (Google what this looks like if you don't know). Hold the compressed air can upright and fire in short bursts. Do not shake it. Do not hold it sideways, do not tip it.
Once the inside of the computers are clean, download the following software onto both of them:
AVAST Free antivirus
www.avast.com
RKill
www.bleepingcomputer.com/download/rkill/
ADWCleaner
https://toolslib.net/downloads/viewdownload/1-adwcleaner/
MalwareBytes
www.malwarebytes.org
Install Avast Antivirus, it comes with a "safezone" browser. Use that as your web browser from now on as it is more secure. Update Avast to the latest virus definitions, then click on scan and select boot time scan and let it run.
Next run Rkill, then, without restarting your PC, run ADWcleaner, then install and run Malwarebytes and do a custom scan including rootkit scan.
This will get rid of (most) viruses and malware and (should) solve your problems. From then on, it's up to you to be a careful internet user, be careful what and where you download, avoid chain emails with stupid jokes and attachments, avoid pornographic websites (pretty much all of them are out to get you somehow with few exceptions. There are safe-ish ones but they often link to others which are not safe), etc.
If the above does not solve your problem, you can do a factory reset of your windows installations (Google how to do this. I don't want to type that much and it is very straight forward). This will give you a "new" machine/machines with no bad stuff on them, except maybe some bloatware (unnecessary programs that come with name brand computers) which you can remove from the control panel.
After you do a factory reset, take precautions to use your computers safely, and install Avast free antivirus and use the safezone browser.
It is worth mentioning that no free antivirus is as good as a full payed antivirus, and while avast is a good free package, their paid package is not as good as the paid packages from Bitdefender or Kaspersky. You can get 2 licenses of Bitdefender for under $60 (sometimes way under) and it would be worth your while to invest in that software.
Having said all that, if you manage to get your computers under control and you feel like they just aren't fast enough for you once they're clean, you can consider buying new machine(s) but I honestly don't think that will be necessary. Keep in mind that upgrades are also possible. You can add more memory or an SSD and we can teach you how to do that. I seriously doubt you need to purchase two new computers right now.
HTH
BTW don't say words like c__k on forums the mods don't like that. I don't mind but I dont want you to get in trouble. Kids read these forums.
PS if you want to buy a new computer(s) I agree that you might want to try them in store to see that they are fast enough for you and can handle what you want to do with them, but I would steer you away from places like BestBuy for that kind of thing, as they tend to have VERY ignorant (know nothing-types) people selling computers who don't know anything about what they're selling other than the fact that selling you a $2000 computer = higher commission for them than selling you a $500 computer, which is probably going to be fast enough for you anyways.
While it's not a bad idea to try computers in a store to see that certain combinations of hardware are fast for you (ie, cpu X with X amount of memory and X storage layout) but I would argue that you are better off buying from either a specialty store such as a Fry's/Circuit City (they aren't even around any more though I dont think) or buying online from a site like Newegg.
If you are in Canada you can go to an NCIX or Canada computers store and they won't screw you around. However, be careful, and don't buy anything without running the specs and price by us here first. Unfortunately, this industry prays on the ignorant and ESPECIALLY on seniors. I have worked in computer shops (as an unpaid apprentice) and I have seen some serious stuff go down. I saw a 60-something year old man who didn't know a mouse from a rat get sold a Pentium 4 machine (this was this year by the way, so 13 year old+ machine) for $200. It was worth MAYBE $20 and that's being generous.
