My account was deleted all the sudden. I had ONLY gifts from my friends on it.
Seems like GOG does not like this ! Be careful everyone.

I have reinstall my OS and made a backup of my saves.
I wanted to continue my playthrough just to find out my account has been DELETED.

I had a good library from gifts i received.
How secure is this site ? regarding accounts when you pay for games and after you can LOSE all of them just like that.

Contact support. There have been cases of hijacked accounts, with email and password changed.

I will try that. But i don't think it was hijacked because i have a very good anti-virus which has internet security.

What game(s) were on your account?

I don't think that's relevant.

Do you remember your account's name? Did you check your e-mail to see whether you received a message from GOG telling you that your password has been changed?

No email with password change. Yes i remember it.

The anti-virus will only protect you from threats on your computer. Phising and/or guessing your password is still possible, even if your computer never had any malware issues, especially if you used the same password in multiple sites.

Yep, support is the answer. Depends where these 'gifts' came from, too; as GOG should be the only place people buy gifts from. Resellers are unauthorised.

As for your last line, you just said someone gifted you the game, now you're saying you paid for it. Which is it?

I never use the same password on different sites.

Then, you should go here: http://www.gog.com/support/contact/general_website_questions and explain your issue as best as possible to support.

It could be, as some games purchsed on G2A are removed from accounts because the keys were provided to G2A through stolen credit cards.

Just trying to clarify though: you're saying the actual account no longer exists at all?

GOG doesn't just delete accounts though. So this is some odd glitch in all likelihood. As JMich suggested, Support is the avenue to approach this. Just be aware that it's the weekend and support doesn't work ont he weekend.

I was asking if that happens when you have gifts only it could easily happen when you pay for them and lose them afterwards.
Correct.

Well then no, accounts do not get deleted after legitimate purchases.

Sorry to hear about the loss

"
15. TERMINATION

If you seriously breach this Agreement you may lose access to GOG.com (temporarily or permanently). In the very unlikely situation that we have to stop running GOG.com we'll do our best to give you advance notice, so that you can download and safely store all your DRM­free content.

15.1 We may cancel or suspend your access to GOG services and GOG content if you materially breach this Agreement. We'll try reasonably to contact you to explain why we've done this and what (if anything) you can do as a result. It seems very unlikely, but if we have to stop providing access to GOG services and GOG content permanently (not because of any breach by you), we will try to give you at least sixty (60) days advance notice by posting a note on www.gog.com and sending an email to every registered users – during that time you should be able to download any GOG content you purchased.

6.2 If we cease providing GOG services or GOG content, or if your use of them is cancelled or suspended because of your breach, then we will not have any future obligations to you – including to offer refunds or payments.
"

If your account has been deleted then you need to contact support.ASAP. They should have contacted you before deletion, and should have 30 days worth of back up to protect your account. A bit of luck as you wont get any response from them until Monday at the earliest. You may also require the confirmation email that the games were activated.

There is one problem. If your account only has games that have been gifted and it turns out the other person(s) was using stolen / fraudulent cards then they may have been forced to remove those games as stolen property. People have lost games in the past because the code used to activate them is later deactivated as it was bought fraudulently.