im not sure if it is CPU How do I check it?
Not to fear, $700 is enough to get a pretty good PC! Do you only play Blockland on PC or do you play other games or plan to other games on your PC?
Here are a list of parts from Newegg.com
Motherboard: ASRock H77M LGA 115 $70
Processor: Intel core i3 3200 Ivy Bridge (3.3ghz --pretty fast) $120
RAM: 8GB DDR3 1333mhz GSkill $39
Case: NZXT Source 210 $39
DVD Drive: ASUS 24x DVD Drive $19
HDD: Seagate Barracuda 1TB SATA 3 7200rpm $79
PSU: CX430w 430W $45
Graphics Card: HIS AMD 7770 $134
OS: Windows 7 Home Premium OEM $99
Total: $659.91 (without tax, put in your zip code to see how much it is with tax, it will probably be around $30 or so)
You got yourself a nice gaming PC right there! You can upgrade your ram to 16GB, you can also upgrade your processor to even an i7 later.