I need to send my laptop in for some warranty repair work and I was wondering what I can do to protect my personal information. Does anyone have any suggestion?

What's the nature of the warranty work?

delete the nude pictures and homeporn, burn the hdd :)

i think if somebody really wants your personal informations he will get it, but hdd format is useful

If you cant turn it on, then other than taking the hdd out I don't see how you could. If you can turn it on, then copy all files to an external device, clear your browser history/cache clear temporary files. Things you should really be doing all the time anyways. I tend not to keep anything personal on the computer, but on removable media. And security process such as clear browser on exit will prevent auto loggins. Oh, and change all your passwords which may have been obtainable once you get the computer back, you should change the regularly anyway.

Is the laptop still running? If so you could encrypt those parts for your eyes only and delete all other informations (like history of visited sites....and make sure they are deleted, not with dumbing them in the bin only).

If the laptop isn't running, you must open it and remove the HDD. Could be a little tricky for the company to check it now ;-)
So if possible change the HDD with another one.

Oh, and the radical way...format c:/s

easy way. pull the hdd out, and tell em.

Nuke it.

The battery is not holding a charge or charging. Lenovo thinks it could either be the cord, Motherboard or battery. yeah I thought about doing that but I'm thinking it a little overkill.

As others said, just take the HDD out. Discuss with support how to do it so it does not void the warranty. Unfortunately for you, might be a catch 22 of sorts. Your concern is reeasonable, yet I'm not sure how many manufactures / sellers have the procedures in place for this.

Okay, that's why I asked, and Brasas took it where I was going to go with it. If it's something that doesn't specifically require the HDD (such as your battery charging problem) then ask if you can remove it prior to sending it in. From a technical standpoint I don't see why they would have a problem with doing so, but the warranty policy might not be that flexible. But I would certainly ask.

I know ;)
It all depends on how badly you want whatever is on there secret.
Me, I don't care if people see all my weird fetishes.
I don't have a credit card so they can't steal that, I suppose I might remove all my cookies and such just in case.
Obviously if your profile and/or your entire drive is encrypted that won't be an issue.
You could also create an encrypted volume and move all your sensitive data there until you get the laptop back.
But since the Truecrypt debacle I haven't really kept up with encryption software.
Way back when it was my last day at a company I nuked my drive and installed Linux on it though.

This remember for a few years back, i was in visit at an company, while i was leaving, in the parking lot, there was an USB flash stick lying around. Took it, tried it out in an PC, it was having all kind of work-related stuff on it and, around all that, an folder called "DO NOT OPEN" or something like it. Of course i opened it, just to find out some nude pictures of a girl with who i talked earlier. I did not returned that stick.

Now, to answer the OP, clear browser data and move your personal data over. Now, depends what do you understand by "personal data". I keep all kind of stuff on my personal PC, from my bank accounts to passwords, scans from my personal documents, so, of course, i would remove those, put them on an USB flash, if i would let anyone else handle my PC. But other than that, i wouldn't care for other things and, trust me, the guys that handle your PC don't usually care either, like photos or stuff like that.
Other than that, most companies that do this kind of work need to have some kind of confidentiality agreement. Your battery problem might need the HDD to be in, with an working operating system. They might need to check the levels, how fast does it drain, it's easier from OS. If you bought the laptop from them, most likely you are not allowed to open it up and remove the HDD and, let's be frank, it's not as easy to do as on an desktop PC. If you don't know what you are doing, you might mess things up. So, you better don't worry too much about it. The technicians don't usually have time to search over your computer and watch your holiday pictures. They pretty much do their job and that's it.

When in doubt: https://www.youtube.com/watch?v=aCbfMkh940Q

pics or it didn't happen.

Yes, our government regularly leave vast amounts of confidential information lying around. The usb I use really only has passwords, the usb is encrypted (hardware), and keepass for the passwords. By the time someone might crack it, I would have changed all of them. I keep all my non personal stuff on multiple hdds which only get plugged in at 3 month backup periods, they are stored externally to the place. Bank details are never stored anywhere electronically. All basic processes you should be doing.

But yes, I doubt the repair guy is that interested. Its just about getting to a personal comfort level.