A password on a windows computer has some security value but it is by-no-means an inpenetrable way to protect your data. Putting a password on the login to your computer will make it harder for indidividuals with physical access to it to interfere with your files and settings, but there are still many, many ways that a sufficiently skilled individual with physical access can get into your admin account and from there read everyting on your machine or modify your settings or files.
As for the more common threat, remote attacks and malware i don't think the presence of a password has much effect, but i might be wrong about this, especially if you have anything like UAC enabled.
The main thing a windows password will do is keep honest people honest and stop anyone who has a few minutes alone with your computer from changing it's settings or prying into your files, but if an attacker has physical access for more than 20 minutes or so and reasonable skill then the windows password won't offer much protection.
There are good reasons for the password to logon to the admin account of a windows machine not to be impossible to bypass, afterall computer repair shops need to be able to "unlock" machines when the owners forget their passwords.
If you have prvate data on the device you should consider encrypting it within an encrypted volume (i don't know much about them) or within an encrypted archive, i use these in the form of 7z archives. This should have a long hard to guess password and not be the same as your windows one. If you use that method then although an attacker with physical access, time and skill could hack your machine/delete files/install malware they could NOT read your private files as the encryptions protecting archives and volumes are usually pretty un-breachable. What's more if your forget the pasword you are not locked out of your whole pc (you can stil run programs, browse the web and read your less private files which you didn't encrypt), just locked out (for all eternity unless you remember that password) from the few (or many) private files you chose to encrypt. In the case of remote attacks these encrypted archives are just as tough as for attacks by physically present snoopers, AND AS LONG AS there is not an incident where the attacker (remote or local) installs a keylogger which you don't realise the existence of until after it has watched you entering your password to the private archive/volume then the private files will stay private.
I would suggest you have a password for logging into the admin account of your machine, but it needn't be a superstrong (though it's a good idea to use a reasonably strong one: longish, not a dictionary word, not an insult or other profanity, not a football team, not a friend/familymember/pet, not anything based on "password", not "letmein" or "openup", have a few letter for number substitutions) one and it would be safe to write down as long as the written copy is kept in a locked safe or something. For private data it should go in an encrypted archive/volume whose password should NEVER be written anywhere and must be very strong. This method of encrypting the private archve/volume would ensure even the computer repair shop couldn't read your private documents if you ever needed to take your machine in for anything, and the encrypted archive could be backed up onto USB sticks and it's security wouldn't be compromised by doing so.
I use 7z for making encrypted archives, if you want to go down the "volumes" route there is a famous piece of software called truecrypt however there have been recent questions asked about it's security because it's own developers claimed it was no longer secure despite independent programmers looking over it's open source code and verifying it was safe, as yet it's not proven which side was correct in that debate.
Edited by rp88, 28 January 2015 - 07:31 PM.
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB