Help! Budget CDs that wont work!?

i bought 50 emtec brand cds at Harvey Norman for NZ$9.99. they are 52x cd-r shrink wrapped. They work on my HP desktop computer but when i put them in my HP laptop, they just rattle in the bay and cant read. They also wont play on my home theatre cd player, but will play on my portable cd player. on the packaging there is a site for web istance (www.emtec-webistance.com) but it seems that it isnt there. i can take them back because ive already used two. any ideas why they wont work? i would be very grateful to the person who helps. if you require any additional information, please ask. thank you!