Is it safe? virus bypassed avast, zone alarm, can I trust scans now?

Hi everyone,
I’m trying to figure out whether or not my laptop is now “clean” and could use some advice.
I’m decently careful with security and viruses. I run avast! and Zonealarm, Malwarebytes anti-malware as a backup scanner and use web of trust when online. However something rather disconcerting happened.
Here’s the story:
Last night, my computer started running excruciatingly slow. Opera stalled and crashed. Even my calculator started lagging. With a fresh, three-day-old Windows 7 install and a fairly quick computer, the problems surprised me.
Then I checked my security panel.
Somehow, something had shutdown every piece of security software I had. Avast’s shield, Zonealarm, Windows Firewall – the works. I couldn’t start them up again.
Virus. And I hadn’t gotten so much as a beep.
I shut down and restarted in safemode. I ran full scans with both Avast! and Malwarebytes. Zilch. Neither picked up anything.
Next, I tried to run an Avast! boot scan, but it wouldn’t load. Windows just started normally, and then my computer shutdown as if someone had pulled the plug.
I tried again. Safemode. Bootscan. Restart. This time, the scan did start, but about thirty seconds in, my laptop cut off just as it had before.
Finally, I loaded in repair mode and used system restore. Now, everything seems to work fine. I ran scans after logging in and nothing showed up. It did seem to lag at first, but not like before. I’ve written that off as post-viral paranoia.
So here’s my question:
Should I trust that everything’s fixed? The system restore point couldn’t have been from more than ten minutes before the problems started. Between the restore point and the crash, I didn’t download anything or visit any sketchy websites. I watched Hulu. Also, I did a quick scan and found two newly opened ports: 445 and 25. I’m still a novice and could be wrong, but that seems sketchy.
Is it possible I’m still infected? Given that this bug out-muscled and evaded everything I’ve got before, should I trust the scans now? As mentioned, I just installed Windows, so it wouldn’t be a huge loss to reinstall, just a huge annoyance. Do you think that’s necessary? Any other suggestions?

Sorry about the long post, but I wanted to be thorough. Like I said, I’m still learning this stuff, so I really appreciate your help.

Thanks in advance
Frank

Firstly I would remove ZoneAlarm as it has caused a lot of problems lately.

If you want a software firewall Outpost is quite good:
http://free.agnitum.com

Also Web of Trust is run by a bunch of users that have many biases that are unfounded so I recommend Finjan SecureBrowsing
http://securebrowsing.finjan.com

Its from M86 Security:
http://www.m86security.com

Will do. Thanks for the really quick response.

What type of laptop is this?

I know that you’ve freshly installed Windows 7, but you could run some diagnostics on it depending on the manufacturer to see if a fan or a hard drive has failed.

It’s odd that all of the scans found nothing, and after a “repair mode” everything seems to be working fine.

The problem is what caused the problem in the first place? Bad memory, HDD, or software? High temperatures, or corrupt software?

Only diagnostics and a lot of time running them will fully solve it. Unless of course it continues running normally for a while…