Display distorted

I connected my laptop to my TV by HDMI and had to adjust the display settings on my laptop to synchronise with the TV. All fine, but now I've disconnected I can't get my laptop display back to the way it was. I only have the options of 1024x768 or 800x600 pixels, neither of which are the same display as I had before (I didn't note down what they were unfortunately.)
It's a Dell netbook and I know that display options on these are limited.

Are you SURE you aren't being offered more options?

Reboot the laptop.

Usually putting the slider up to the top is where it should be on a LCD-type screen.

If you go into screen resolution there is an option to Detect the monitor.

Thank you for replying so quickly. Yes, I've tried those options and still get the distortion. I definitely just get the two 'pixel' choices. By the way, the netbook in question is a Dell Mini (I don't put it in my signature as I usually only use it to take away on trips etc.) If I had to describe it, I'd say that it's all a bit 'elongated'. Perfectly legible and I can live with it, but I'm curious about how this happened. I know that at work when we plug a computer into an interactive board the display is temporarily similar but then goes back to the original size. Anyway, I'll have another go at resolving this tomorrow.
Footnote: I've just tried my Admin account and there are more display choices in 'My Computer' so it's a case of trial and error, I fear. Aren't computers wonderful!!