Extremely Sluggish Internet - Running Out of Options

Hi, guys.

At first this may sound like a common issue, but I've tried a number of solutions to overcome this from other posts which may be similar to mine. Sadly, none of the solutions has worked. So, let me describe my system's status.

I have an HP Pavillion laptop, running on Windows Vista 32bit and 4gig memory. Just this week, my internet on this system became very, very slow. It takes about 20 mins just to load my Google homepage. And this was not a progression. It all happened so suddenly. Not just in Firefox but IE7 as well, including my Outlook, so it's not a browser issue. All 4 PCs in our house are running on wireless network, but only my laptop has this issue. The 3 others (2 XPs and another Vista) have fast connections. This has been our setup for years now, so overloading on the network should be cancelled out.

Here are the troubleshooting attempts I've made:
1. I turned off all Add-ons but it didn't work
2. I've updated my browsers.
3. I've ran updated antivirus, anti-malware and Windows Defender, nothing.
4. I've turned off TLS protocols in the advanced setting.
5. I've turned off Vista's autotuning through the command prompt. Didn't work.

I'm running out of options. Is there anything I haven't covered?

6. Browsing history, search history, cookies, cache, active logins have all been cleared.

*Sorry, I have IE8, but I don't think it matters anyway. And local programs are running well.

try this in command prompt: ipconfig /flushdns

Also, try disabling antivirus/anti-malware software and see if it improves. What AV do you use?