How do I tell if I have a virus or just battery issues?

It cannot be a virus as none exist for Macs.

Post an etrecheck report for analysis.

Pete

Click on the blue etrecheck link, read the directions on the site and then post the results back here. It is safe, will not post any personal details and may give an indication of what may be causing your issue. There are more complex ways to try to resolve your issue, but an etrecheck gives a quick way to remedy any 'obvious' third party conflicts.

Cheers

Pete

How are you posting here? On a phone? If so, then not much can be done without you having internet access to your Mac. Take it to your nearest Apple Store for analysis/repair.

Pete

Try booting to Safe mode and repairing the HD

OS X: What is Safe Boot, Safe Mode?

If still problem

Boot to Recovery and repair the HD

OS X: About OS X Recovery - Apple Support

Reinstall Yosemeite

OS X Yosemite: Reinstall OS X

Last do a fresh install of Yosemite via Recovery

It sounds like a battery issue. On a laptop it is underneath, under a removable panel. You should need tools.

But it will depend on the year of the laptop if this is a problem to be easily fixed. Most laptops will remain operational while plugged in, no matter the condition of the battery.

A good test is to boot the computer, check the battery level, and then unplug from the charger. If the computer shuts down, then its the battery. Some laptops register a full battery or half charge when the battery can't charge at all, its just pass due.

Batteries are easily replaced but usually cost around 200 bucks.

Sorry, - you SHOULDN'T NEED TOOLS, not should, my bad

How do you get the screws out?

Pete

EveryUserName HasBeenTaken wrote:

It sounds like a battery issue.

No, it really doesn't. There is absolutely no way that a battery issue would cause all logins to fail except for the Guest login.

lakegigi wrote:

So a few days ago I let my MacBook die, when I tried turning it back on the next morning it would shut off as I logged into my account.

It sounds like something is badly wrong with your system. It is not a virus, nor is it related to the battery. (You may or may not also have battery issues, but if it were a battery problem, it would affect all users and wouldn't affect you if you had the machine plugged in to a power outlet, as you describe.)

Do you have Time Machine backups? If so, you may want to restore your system to a state prior to when this problem occurred. See:

How do I restore my entire system?

If you don't have Time Machine backups, do you have any backups at all?

petermac87 wrote:

It cannot be a virus as none exist for Macs.

How are you so sure ?

Grane Duke wrote:

petermac87 wrote:

It cannot be a virus as none exist for Macs.

How are you so sure ?

Because there are no OSX viruses, easy really.

None have ever been reported. Can you provide a link to one? Or are you just here to stir the pot as you usually do? 😉

Pete

EveryUserName HasBeenTaken wrote:

Sorry, - you SHOULDN'T NEED TOOLS, not should, my bad

Do you have any idea what you are talking about, if you don't have tools you can not change the battery.

time to do a little research before posting.