SD card works on camera, but not computer?

I have an SDHC Card, and I use it with my Nikon camera almost every day, and every day I put my SD card into my HP Pavilion laptop and it works, and I store the pictures in different folders on my computer. Recently, I have to push the SD Card in pretty hard until it reads, but today, no matter how hard I try, it won't work. I also tried the SD card in my brother's laptop, and it wouldn't read.So the card won't work in two laptops, but it still reads perfectly fine on my camera. I don't have the USB for the camera.
>>> SD card works on camera, but not computer?

Sigma 70-200mm f/2.8 D EX Lens is work as nikon AFS Len?

Sigma 70-200mm f/2.8 D EX Lens is work as nikon AFS Len?
>>> Sigma 70-200mm f/2.8 D EX Lens is work as nikon AFS Len?

Why is my flash doing this to my pictures?

I just got a neewer flash for my nikon. I was just shooting and the bottom of my picture burns out black. Why? What do I need I do?
>>> Why is my flash doing this to my pictures?

My camera goes blank when I take a picture!

I just got my Nikon 21x zoom camera yesterday (not a new one) and it was working fine, it just dies really fast.
Anyways, I took a picture, but then it just goes to a black screen, still on! But black. Whyyyyy? D: I switched the batteries a jillion times, erased some pictures and videos I didn't need but still… same thing.
>>> My camera goes blank when I take a picture!

Are canons worth the extra money compared to nikon?

Are canons worth the extra money compared to nikon?
>>> Are canons worth the extra money compared to nikon?

Help with High Speed Sync Flash? (Lumopro 160)?

I bought my first external flash and have been happy with it until now.My goal was always to do low key photography but only NOW have i learned about high speed sync flash.

I dont even understand the concept entirely. Can someone put it in laymans terms?

Also, is there anyway to do low key photography with my flash or no? Should I invest in another flash? Do I have to buy an expensive flash to achieve low key results?

(I have a nikon d3000.)

Thanks in advance…
5 stars
>>> Help with High Speed Sync Flash? (Lumopro 160)?